Delete stale.yml

Remove the stale github action.

.github/workflows/stale.yml

@@ -1,19 +0,0 @@
-name: Mark stale issues and pull requests
-
-on:
-  schedule:
-  - cron: "0 0 * * *"
-
-jobs:
-  stale:
-
-    runs-on: ubuntu-latest
-
-    steps:
-    - uses: actions/stale@v1
-      with:
-        repo-token: ${{ secrets.GITHUB_TOKEN }}
-        stale-issue-message: 'Stale issue message'
-        stale-pr-message: 'Stale pull request message'
-        stale-issue-label: 'no-issue-activity'
-        stale-pr-label: 'no-pr-activity'