Remove the workflow until we figured out a better workflow (#44749)

.github/workflows/external-pr-label.yml

-name: Mark External PRs
-
-on:
-  pull_request:
-    types: [opened]
-
-jobs:
-  on-pr-opened:
-    permissions:
-      pull-requests: write
-    runs-on: ubuntu-22.04
-    timeout-minutes: 1
-    if: ${{ !contains(github.event.pull_request.labels.*.name, 'External') }}
-    steps:
-      - uses: tspascoal/get-user-teams-membership@v3
-        id: checkUserMember
-        with:
-          username: ${{ github.actor }}
-          organization: 'metabase'
-          team: 'employees'
-          GITHUB_TOKEN: ${{ secrets.METABASE_AUTOMATION_USER_TOKEN }} # Token with read:org scope
-
-      - name: add labels
-        uses: actions-ecosystem/action-add-labels@v1
-        if: ${{ steps.checkUserMember.outputs.isTeamMember == 'false' }}
-        with:
-          labels: |
-            External