Remove first interaction workflow (#9112)

This workflow is currently not function as expected. I'm not sure why it
would not be more clearly documented, but there doesn't seem to be a way
that this would actually work to leave a comment on a first time
contributor's PR (given that the contributor is using a fork)...

Relevant discussions:
https://github.com/actions/first-interaction/issues/10
https://github.community/t/github-actions-are-severely-limited-on-prs/18179#M9249

.github/workflows/welcome.yml

@@ -1,24 +0,0 @@
-# This workflow welcomes new contributors with a message!
-
-# https://github.com/marketplace/actions/first-interaction (https://github.com/actions/first-interaction)
-
-name: "Welcome New Contributor"
-on:
-  pull_request:
-    types: [opened]
-
-jobs:
-  welcome:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/first-interaction@v1.0.0
-        with:
-          repo-token: ${{ secrets.GITHUB_TOKEN }}
-          pr-message: |-
-            Congrats on making your first Pull Request to Forem! 🎉
-
-            Our core team will review your proposal as soon as possible. Our [code review process is publicly documented](https://docs.dev.to/maintainers/pull_requests/), so you'll know exactly what to expect.
-
-            If you haven't had a chance, give our [Contributing Guide](https://docs.dev.to/contributing/forem/) a read.
-
-            Thanks for taking the time to improve our platform and our community! ❤️