ci: Remove PR tracking action

.github/workflows/track_merged_prs.yml

@@ -1,17 +0,0 @@
-name: Track merged pull requests
-
-on:
-  pull_request:
-    types:
-      - closed
-
-jobs:
-  add-to-project:
-    if: github.event.pull_request.merged == true
-    name: Add pull request to project
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/add-to-project@v0.5.0
-        with:
-          project-url: https://github.com/orgs/ruffle-rs/projects/7
-          github-token: ${{ secrets.RUFFLE_BUILD_TOKEN }}