Remove GitHub action for syncing main branch with master

.github/workflows/sync-main-branch.yml

@@ -1,26 +0,0 @@
-# Synchronize all pushes to 'master' branch with 'main' branch to facilitate migration
-name: "Sync main branch"
-on:
-  push:
-    branches:
-      - master
-
-jobs:
-  sync_latest_from_upstream:
-    runs-on: ubuntu-latest
-    name: Sync latest commits from master branch
-
-    steps:
-      - name: Checkout target repo
-        uses: actions/checkout@v2
-        with:
-          ref: main
-
-      - name: Sync upstream changes
-        id: sync
-        uses: aormsby/Fork-Sync-With-Upstream-action@v3.0
-        with:
-          target_sync_branch: main
-          target_repo_token: ${{ secrets.GITHUB_TOKEN }}
-          upstream_sync_branch: master
-          upstream_sync_repo: elastic/elasticsearch