Revert "Add Sponsor Labels action"

This reverts commit 845034c81c.

.github/workflows/label-sponsors.yml

@@ -1,14 +0,0 @@
-name: Label sponsors
-on:
-  pull_request:
-    types: [opened]
-  issues:
-    types: [opened]
-jobs:
-  build:
-    name: is-sponsor-label
-    runs-on: ubuntu-latest
-    steps:
-      - uses: JasonEtco/is-sponsor-label-action@v1.2.0
-        env:
-          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}