ci: remove incorrect comment from codegen workflow

PR #14883 fixed the codegen workflow but introduced a comment
that is simply wrong.

This change rectifies this mistake by removing the comment.

Signed-off-by: Michael Adam <obnox@samba.org>
(cherry picked from commit 714f80a80a)

.github/workflows/codegen.yml

@@ -51,7 +51,5 @@ jobs:
 
       - name: validate codegen
         run: |
-          # run validation again, explicitly.
-          # it is also part of 'make codegen'
           cd $(go env GOPATH)/src/github.com/rook/rook
           tests/scripts/validate_modified_files.sh codegen