Delete mirror-master-and-main.yml

Closes #1865

.github/workflows/mirror-master-and-main.yml

@@ -1,21 +0,0 @@
-name: Mirror "master" and "main" branches
-on:
-  push:
-    branches:
-      - master
-      - main
-
-jobs:
-  mirror:
-    runs-on: ubuntu-latest
-    steps:
-      - name: Mirror to "master"
-        uses: zofrex/mirror-branch@ea152f124954fa4eb26eea3fe0dbe313a3a08d94
-        with:
-          target-branch: master
-          force: false
-      - name: Mirror to "main"
-        uses: zofrex/mirror-branch@ea152f124954fa4eb26eea3fe0dbe313a3a08d94
-        with:
-          target-branch: main
-          force: false