[Security Solution] remove donutChartEmbeddablesEnabled feature flag and related code (#240393)

## Summary

This PR removes the `donutChartEmbeddablesEnabled` feature flag and its
related code. This feature flag was last touched mid 2023 and hasn't
seen any traction since.

> [!IMPORTANT]
> As the feature flag has been `false` for the last couple of years, no
UI or behavior changes should be introduced by this PR!

### Checklist

- [x] The PR description includes the appropriate Release Notes section,
and the correct `release_note:*` label is applied per the
[guidelines](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)
- [x] Review the [backport
guidelines](https://docs.google.com/document/d/1VyN5k91e5OVumlc0Gb9RPa3h1ewuPE705nRtioPiTvY/edit?usp=sharing)
and apply applicable `backport:*` labels.

Author: PhilippeOberti

x-pack/platform/plugins/private/translations/translations/de-DE.json

@@ -36668,7 +36668,6 @@
     "xpack.securitySolution.entityAnalytics.riskDashboard.viewAllLabel": "Alle anzeigen",
     "xpack.securitySolution.entityAnalytics.riskEngine.missingIndexPrivilege": "Fehlende Indexberechtigungen für den Index \"{indexName}\": {privileges}.",
     "xpack.securitySolution.entityAnalytics.riskEngine.unauthorized": "Dem Nutzer fehlen die Berechtigungen für die Risiko-Engine.",
-    "xpack.securitySolution.entityAnalytics.riskScore.chart.totalLabel": "Gesamt",
     "xpack.securitySolution.entityAnalytics.riskScore.donut_chart.totalLabel": "Gesamt",
     "xpack.securitySolution.entityAnalytics.usersRiskDashboard.title": "{entityType} Risiko-Scores",
     "xpack.securitySolution.entityDetails.userPanel.error": "Bei der Berechnung des Risiko-Score für {entity} ist ein Problem aufgetreten",

x-pack/platform/plugins/private/translations/translations/fr-FR.json

@@ -36887,7 +36887,6 @@
     "xpack.securitySolution.entityAnalytics.riskDashboard.viewAllLabel": "Afficher tout",
     "xpack.securitySolution.entityAnalytics.riskEngine.missingIndexPrivilege": "Privilèges d'index manquants pour l'index \"{indexName}\" : {privileges}.",
     "xpack.securitySolution.entityAnalytics.riskEngine.unauthorized": "L'utilisateur ne dispose pas des privilèges requis pour modifier le moteur de risque.",
-    "xpack.securitySolution.entityAnalytics.riskScore.chart.totalLabel": "Total",
     "xpack.securitySolution.entityAnalytics.riskScore.donut_chart.totalLabel": "Total",
     "xpack.securitySolution.entityAnalytics.usersRiskDashboard.title": "Scores de risque de {entityType}",
     "xpack.securitySolution.entityDetails.userPanel.error": "Une erreur a été rencontrée lors du calcul du score de risque de {entity}",

x-pack/platform/plugins/private/translations/translations/ja-JP.json

@@ -36927,7 +36927,6 @@
     "xpack.securitySolution.entityAnalytics.riskDashboard.viewAllLabel": "すべて表示",
     "xpack.securitySolution.entityAnalytics.riskEngine.missingIndexPrivilege": "インデックス\"{indexName}\"のインデックス権限が不足しています：{privileges}。",
     "xpack.securitySolution.entityAnalytics.riskEngine.unauthorized": "ユーザーにはリスクエンジン権限がありません。",
-    "xpack.securitySolution.entityAnalytics.riskScore.chart.totalLabel": "合計",
     "xpack.securitySolution.entityAnalytics.riskScore.donut_chart.totalLabel": "合計",
     "xpack.securitySolution.entityAnalytics.usersRiskDashboard.title": "{entityType}リスクスコア",
     "xpack.securitySolution.entityDetails.userPanel.error": "{entity}リスクスコアの計算中に問題が発生しました",

x-pack/platform/plugins/private/translations/translations/zh-CN.json

@@ -36911,7 +36911,6 @@
     "xpack.securitySolution.entityAnalytics.riskDashboard.viewAllLabel": "查看全部",
     "xpack.securitySolution.entityAnalytics.riskEngine.missingIndexPrivilege": "缺少索引“{indexName}”的索引权限：{privileges}。",
     "xpack.securitySolution.entityAnalytics.riskEngine.unauthorized": "用户缺少风险引擎权限。",
-    "xpack.securitySolution.entityAnalytics.riskScore.chart.totalLabel": "合计",
     "xpack.securitySolution.entityAnalytics.riskScore.donut_chart.totalLabel": "合计",
     "xpack.securitySolution.entityAnalytics.usersRiskDashboard.title": "{entityType} 风险分数",
     "xpack.securitySolution.entityDetails.userPanel.error": "计算 {entity} 风险分数时出现问题",

x-pack/solutions/security/plugins/security_solution/common/experimental_features.ts

@@ -12,8 +12,6 @@ export type ExperimentalFeatures = { [K in keyof typeof allowedExperimentalValue
  * This object is then used to validate and parse the value entered.
  */
 export const allowedExperimentalValues = Object.freeze({
-  donutChartEmbeddablesEnabled: false, // Depends on https://github.com/elastic/kibana/issues/136409 item 2 - 6
-
   /**
    * This is used for enabling the end-to-end tests for the security_solution telemetry.
    * We disable the telemetry since we don't have specific roles or permissions around it and

x-pack/solutions/security/plugins/security_solution/public/entity_analytics/components/entity_analytics_risk_score/chart_content.test.tsx

@@ -9,6 +9,7 @@ import { EuiFlexGroup, EuiFlexItem, EuiPanel } from '@elastic/eui';
 
 import { useExpandableFlyoutApi } from '@kbn/expandable-flyout';
 import type { RiskSeverity } from '../../../../common/search_strategy';
+import { EMPTY_SEVERITY_COUNT } from '../../../../common/search_strategy';
 import { useQueryInspector } from '../../../common/components/page/manage_query';
 import {
   EntityPanelKeyByType,
@@ -31,7 +32,6 @@ import { Loader } from '../../../common/components/loader';
 import { Panel } from '../../../common/components/panel';
 import { useEntityInfo } from './use_entity';
 import { RiskScoreHeaderContent } from './header_content';
-import { ChartContent } from './chart_content';
 import { useNavigateToAlertsPageWithFilters } from '../../../common/hooks/use_navigate_to_alerts_page_with_filters';
 import { getRiskEntityTranslation } from './translations';
 import { useKibana } from '../../../common/lib/kibana';
@@ -43,6 +43,7 @@ import { useMissingRiskEnginePrivileges } from '../../hooks/use_missing_risk_eng
 import { EntityEventTypes } from '../../../common/lib/telemetry';
 import { RiskScoresNoDataDetected } from '../risk_score_no_data_detected';
 import { RiskScoreHeaderTitle } from '../risk_score_header_title';
+import { RiskScoreDonutChart } from '../risk_score_donut_chart';
 
 export const ENTITY_RISK_SCORE_TABLE_ID = 'entity-risk-score-table';
 
@@ -220,14 +221,7 @@ const EntityAnalyticsRiskScoresComponent = <T extends EntityType>({
         {toggleStatus && (
           <EuiFlexGroup data-test-subj="entity_analytics_content">
             <EuiFlexItem grow={false}>
-              <ChartContent
-                dataExists={data && data.length > 0}
-                kpiQueryId={entity.kpiQueryId ?? ''}
-                riskEntity={riskEntity}
-                severityCount={severityCount}
-                timerange={timerange}
-                selectedSeverity={selectedSeverity}
-              />
+              <RiskScoreDonutChart severityCount={severityCount ?? EMPTY_SEVERITY_COUNT} />
             </EuiFlexItem>
             <EuiFlexItem>
               <StyledBasicTable