remove unused docs substitution variables (#2831)

Author: shainaraskas

docset.yml

@@ -88,7 +88,6 @@ subs:
   eck:   "Elastic Cloud on Kubernetes"
   edot:  "Elastic Distribution of OpenTelemetry"
   motlp: "Elastic Cloud Managed OTLP Endpoint"
-  edot-cf:   "EDOT Cloud Forwarder"
   serverless-full:   "Elastic Cloud Serverless"
   serverless-short:   "Serverless"
   es-serverless:   "Elasticsearch Serverless"
@@ -114,7 +113,6 @@ subs:
   ems-init:   "EMS"
   hosted-ems:   "Elastic Maps Server"
   ipm-app:   "Index Pattern Management"
-  ingest-pipelines-app:   "Ingest Pipelines"
   ls-pipelines-app:   "Logstash Pipelines"
   maint-windows-app:   "Maintenance Windows"
   maint-windows-cap:   "Maintenance windows"
@@ -148,7 +146,6 @@ subs:
   kib:   "Kibana"
   ls:   "Logstash"
   beats:   "Beats"
-  agentbeat:   "Agentbeat"
   auditbeat:   "Auditbeat"
   filebeat:   "Filebeat"
   heartbeat:   "Heartbeat"
@@ -188,7 +185,6 @@ subs:
   searchprofiler:   "Search Profiler"
   ml:   "machine learning"
   ml-cap:   "Machine learning"
-  ml-init:   "ML"
   ml-features:   "machine learning features"
   stack-ml-features:   "Elastic Stack machine learning features"
   ccr:   "cross-cluster replication"
@@ -272,12 +268,7 @@ subs:
   private-locations:   "Private Locations"
   esh:   "ES-Hadoop"
   observability:   "Observability"
-  api-request-title:   "Request"
-  api-prereq-title:   "Prerequisites"
-  api-description-title:   "Description"
-  api-path-parms-title:   "Path parameters"
   api-query-parms-title:   "Query parameters"
-  api-request-body-title:   "Request body"
   api-examples-title:   "Examples"
   agent-issue:   "https://github.com/elastic/elastic-agent/issues/"
   agent-pull:   "https://github.com/elastic/elastic-agent/pull/"
@@ -288,7 +279,6 @@ subs:
   eck_helm_minimum_version: "3.2.0"
   eck_resources_list: "Elasticsearch, Kibana, APM Server, Beats, Elastic Agent, Elastic Maps Server, and Logstash"
   eck_resources_list_short: "APM Server, Beats, Elastic Agent, Elastic Maps Server, and Logstash"
-  release-date: "2-April-2025"
   heroku: "Elasticsearch Add-on for Heroku"
   obs-ai-assistant: "Elastic AI Assistant for Observability and Search"
   apm-server: "APM Server"