[Github] Remove invalid comment from pr-code-format.yaml

The comment was originally added in
b3af755, but
2898c3e greatly simplified things
making the previous comment invalid. We no longer need to look at
diffing main versus the PR and whether we are doing a two dot or three
dot diff as we are just diffing the merge commit.

Author: boomanaiden154

.github/workflows/pr-code-format.yml

@@ -73,10 +73,6 @@ jobs:
           START_REV: ${{ github.event.pull_request.base.sha }}
           END_REV: ${{ github.event.pull_request.head.sha }}
           CHANGED_FILES: ${{ steps.changed-files.outputs.all_changed_files }}
-        # TODO(boomanaiden154): Once clang v18 is released, we should be able
-        # to take advantage of the new --diff_from_common_commit option
-        # explicitly in code-format-helper.py and not have to diff starting at
-        # the merge base.
         # Create an empty comments file so the pr-write job doesn't fail.
         run: |
           echo "[]" > comments &&