chore: cleanup github action workflows (#522)

- Use consistent label check for external PRs
- Remove unused approved-readme
- Remove unused labels workflow

Author: enocom

.github/labels.yml

@@ -33,7 +33,8 @@ permissions: read-all
 
 jobs:
   analyze:
-    if: "${{ github.event.action != 'labeled' || github.event.label.name == 'tests: run' }}"
+    # Run this job only on PRs that have been labeled
+    if: "${{ (github.event.action != 'labeled' && github.event.pull_request.head.repo.full_name == github.event.pull_request.base.repo.full_name) || github.event.label.name == 'tests: run' }}"
     name: Analyze
     runs-on: ubuntu-latest
     permissions: