Drop the 4.0.x alphas workflow

Now that 4.1.0 is out, 4.0.x binary releases will
no longer be available publicly.

(cherry picked from commit cf98ba5a8c)

Conflicts:
	.github/workflows/release-4.0.x-alphas.yaml

.github/workflows/release-4.0.x-alphas.yaml

@@ -1,35 +0,0 @@
-name: "Trigger a 4.0.x alpha release build"
-on:
-  workflow_dispatch:
-  push:
-    branches:
-      - "v4.0.x"
-    paths:
-      - "deps/*/src/**"
-      - 'deps/rabbitmq_management/priv/**'
-      - ".github/workflows/**"
-      - "rabbitmq-components.mk"
-env:
-  DEV_WORKFLOW_REPOSITORY: "rabbitmq/server-packages"
-jobs:
-  trigger_alpha_build:
-    runs-on: ubuntu-latest
-    steps:
-      - name: Compute prerelease identifier from commit SHA
-        run: echo "PRERELEASE_IDENTIFIER=`echo ${{ github.sha }} | cut -c1-8`" >> $GITHUB_ENV
-      - name: Trigger a 4.0.x alpha build in ${{ env.DEV_WORKFLOW_REPOSITORY }}
-        uses: peter-evans/repository-dispatch@v3
-        with:
-          token: ${{ secrets.MK_RELEASE_AUTOMATION_TOKEN }}
-          repository: ${{ env.DEV_WORKFLOW_REPOSITORY }}
-          event-type: "new_4.0.x_alpha"
-          client-payload: |-
-            {
-              "release_repository": "${{ env.DEV_WORKFLOW_REPOSITORY }}",
-              "release_description": "Commit: https://github.com/rabbitmq/rabbitmq-server/commit/${{ github.sha }}, pushed at: ${{ github.event.repository.pushed_at }}",
-              "prerelease": true,
-              "prerelease_kind": "alpha",
-              "prerelease_identifier": "${{ env.PRERELEASE_IDENTIFIER }}",
-              "release_title": "RabbitMQ ${{ vars.SERVER_40_NEXT_PATCH_VERSION }}-alpha.${{ env.PRERELEASE_IDENTIFIER }} (from ${{ github.event.repository.pushed_at }})",
-              "base_version": "${{ vars.SERVER_40_NEXT_PATCH_VERSION }}"
-            }