Revert "git-commit-checks: comment on PR with error(s)"

[jsquyres]

This reverts commit 4b0ce7e.

FYI @Joe-Downs, per #10632 (comment)

[jsquyres]

It is expected that the Git commit checker (pull_request_target) fails -- that's exactly why this commit is being reverted.

[jsquyres]

I'm going to merge this before CI completes because:

1. we know that one of the CI's is going to fail (that's what revering this commit will fix)
2. this revert is only about the git commit checker -- none of the other CI tests exercise this code
3. might as well get this fix in so that other PR's don't get held up by the broken CI