Remove workflow failure check in favour of Argo-driven version (#25366)

* Simplify workflow failure check

Consolidate the workflow failure check directly into *-master.yml. This results in some code duplication, but makes it much clearer as to what's going on. While we're in here, remove the legacy reference to the `monorepo` branch when triggering.

* just remove the workflow in favour of the Argo version

.github/workflows/workflow-failure-check.yml

@@ -1,19 +0,0 @@
-name: Report on master workflow failure
-on:
-  workflow_run:
-    workflows: [Server CI Master, Web App CI Master]
-    types: [completed]
-
-jobs:
-  on-failure:
-    runs-on: ubuntu-latest
-    if: github.event.workflow_run.conclusion == 'failure'
-    steps:
-      - name: Report failure
-        run: |
-          curl \
-            --fail \
-            -X POST \
-            -H "Content-Type: application/json" \
-            -d "{\"text\":\"#### ⚠️  ${{github.repository}}/${{ github.event.workflow_run.head_branch }} - ${{github.event.workflow_run.name}} build failure ⚠️\\nThe build is failing: [view failure](${{github.server_url}}/${{github.repository}}/actions/runs/${{github.event.workflow_run.id}}).\\n\"}" \
-            ${{ secrets.MM_COMMUNITY_DEVELOPERS_INCOMING_WEBHOOK_FROM_GH_ACTIONS }}