CI: remove labeler workflow and enable webhook-based labeling

Remove the .github/workflows/labeler.yml workflow and enable the "enable_labeler_yml" option in .github/formalities.json to let the webhook bot handle pull request labeling. This avoids running on GitHub Actions, so it is faster and uses fewer resources.

It uses the existing .github/labeler.yml for labels.

Signed-off-by: Josef Schlehofer <pepe.schlehofer@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/24256
(cherry picked from commit 4f2dc5cc64)
Link: https://github.com/openwrt/openwrt/pull/24318
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>

.github/formalities.json

@@ -24,5 +24,6 @@
   "check_makefile_indentation": false,
   "check_pkg_release": "warning",
   "require_linked_github_account": true,
-  "enable_stale_bot": false
+  "enable_stale_bot": false,
+  "enable_labeler_yml": true
 }

.github/workflows/labeler.yml

@@ -1,19 +0,0 @@
-name: 'Pull Request Labeler'
-on:
-  - pull_request_target
-
-permissions:
-  contents: read
-
-jobs:
-  labeler:
-    permissions:
-      contents: read # to determine modified files (actions/labeler)
-      pull-requests: write # to add labels to PRs (actions/labeler)
-
-    name: Pull Request Labeler
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/labeler@v6
-        with:
-          repo-token: '${{ secrets.GITHUB_TOKEN }}'