Revert "[CI] Trigger backports when v* labels are added afterwards (elastic#234452)" (elastic#240946)

## Summary
This reverts commit 040e409 in elastic#234452

Author: delanni

.github/workflows/_fixtures_/github_event_onmerge_1.json

@@ -5,58 +5,22 @@ on:
       - labeled
       - unlabeled
 
-concurrency:
-  group: ${{ github.workflow }}-${{ github.event.pull_request.number }}
-  cancel-in-progress: true
-
 jobs:
   on-merge:
     name: 'Label and Backport'
     runs-on: ubuntu-latest
-    if: github.event.pull_request.merged == true
+    if: |
+      github.event.pull_request.merged == true &&
+        (github.event.action == 'closed' ||
+          (github.event.action == 'labeled' &&
+            (github.event.label.name == 'backport:all-open' ||
+              github.event.label.name == 'backport:version')) ||
+          (github.event.action == 'unlabeled' &&
+            github.event.label.name == 'backport:skip' &&
+            (contains(github.event.pull_request.labels.*.name, 'backport:all-open') ||
+              contains(github.event.pull_request.labels.*.name, 'backport:version'))))
     steps:
-      - run: "echo hello!"
-      - name: Check out versions.json
-        uses: actions/checkout@v5
-        with:
-          repository: 'elastic/kibana'
-          ref: main
-          sparse-checkout: |
-            versions.json
-      - name: Check Event Qualifies
-        uses: actions/github-script@v7
-        id: check_event
-        with:
-          result-encoding: string
-          script: |
-              let shouldRun = false;
-              const backportLabels = { skip: 'backport:skip', allOpen: 'backport:all-open', version: 'backport:version' };
-              const { pull_request: pr, action } = context.payload;
-              const labels = pr.labels.map(l => l.name);
-              const validVersionLabels = require('./versions.json').versions
-                .map(v => v.version.split('.').slice(0,2).join('.'))
-                .map(v => RegExp(`^v${v}\.[0-9]{1,2}$`));
-              const labelsWarrantBackport = labels.includes(backportLabels.allOpen) || (
-                labels.includes(backportLabels.version) &&
-                labels.some(label => validVersionLabels.some(v => v.test(label)))
-              );
-
-              if (action === 'closed') {
-                core.info('PR was merged, proceeding');
-                shouldRun = true;
-              } else if ((action === 'labeled' || action === 'unlabeled') && labelsWarrantBackport) {
-                core.info('labelling action warrants backport, proceeding');
-                shouldRun = true;
-              } else {
-                core.info('event does not warrant backport action, skipping');
-                shouldRun = false;
-              }
-
-              core.info(`Should run on-merge action: ${shouldRun}`);
-              return shouldRun.toString();
-
       - name: Checkout Actions
-        if: ${{ steps.check_event.outputs.result == 'true' }}
         uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
         with:
           repository: 'elastic/kibana-github-actions'
@@ -65,11 +29,9 @@ jobs:
           persist-credentials: false
 
       - name: Install Actions
-        if: ${{ steps.check_event.outputs.result == 'true' }}
         run: npm install --production --prefix ./actions
 
       - name: Run On-Merge
-        if: ${{ steps.check_event.outputs.result == 'true' }}
         uses: ./actions/on-merge
         with:
           github_token: ${{secrets.KIBANAMACHINE_TOKEN}}