Actions: Disable labeler action.

I've left the `labeler.yml` configuration file, in case this ever starts working
properly with forks.

.github/workflows/labeler.yml

@@ -1,11 +0,0 @@
-name: "Pull Request Labeler"
-on:
-- pull_request
-
-jobs:
-  triage:
-    runs-on: ubuntu-latest
-    steps:
-    - uses: actions/labeler@v2
-      with:
-        repo-token: "${{ secrets.GITHUB_TOKEN }}"