CI: remove pullrequest workflow, the GH widget does that

.github/workflows/pullrequest.yml

@@ -1,27 +0,0 @@
-name: pullrequest
-
-on:
-  pull_request:
-    types: [opened, closed]
-
-jobs:
-  notify:
-    runs-on: ubuntu-latest
-    steps:
-      - name: "notify: new"
-        if: github.event.action == 'opened'
-        uses: calamares/actions/matrix-notify@v4
-        with:
-          token: ${{ secrets.MATRIX_TOKEN }}
-          room: ${{ secrets.MATRIX_ROOM }}
-          message: |
-            PR OPENED ${{ github.event.pull_request.html_url }} by ${{ github.actor }}
-            .. ${{ github.event.pull_request.title }}"
-      - name: "notify: closed"
-        if: github.event.action == 'closed'
-        uses: calamares/actions/matrix-notify@v4
-        with:
-          token: ${{ secrets.MATRIX_TOKEN }}
-          room: ${{ secrets.MATRIX_ROOM }}
-          message: |
-            PR CLOSED ${{ github.event.pull_request.html_url }} by ${{ github.actor }}