devops: remove bigsur buildbot (#4457)

.github/workflows/build_webkit.yml

@@ -1,35 +0,0 @@
-name: browser builds
-
-on:
-  push:
-    branches:
-      - master
-    paths:
-      - '.github/workflows/build_webkit.yml'
-      - 'browser_patches/webkit/BUILD_NUMBER'
-
-env:
-  AZ_ACCOUNT_KEY: ${{ secrets.AZ_ACCOUNT_KEY }}
-  AZ_ACCOUNT_NAME: ${{ secrets.AZ_ACCOUNT_NAME }}
-  TELEGRAM_BOT_KEY: ${{ secrets.TELEGRAM_BOT_KEY }}
-
-jobs:
-  build_webkit_mac:
-    name: build webkit @ ${{ matrix.os }}
-    strategy:
-      fail-fast: false
-      matrix:
-        os: [macos-11.0]
-    runs-on: ${{ matrix.os }}
-    steps:
-    - uses: actions/checkout@v2
-    - uses: actions/setup-node@v1
-      with:
-        node-version: 14
-    - uses: microsoft/playwright-github-action@v1
-    - name: setup git credentials
-      run: |
-        git config --global user.name github-actions
-        git config --global user.email github-actions@github.com
-    - run: ./browser_patches/checkout_build_archive_upload.sh webkit-mac-11.0
-