audit: remove incorrect TODO.

This check can't really be in RuboCop (as it relies on the URL strategy
logic).

Library/Homebrew/dev-cmd/audit.rb

@@ -1060,7 +1060,6 @@ module Homebrew
       url_strategy = DownloadStrategyDetector.detect(url)
 
       if using == :git || url_strategy == GitDownloadStrategy
-        # TODO: check could be in RuboCop
         problem "Git should specify :revision when a :tag is specified." if specs[:tag] && !specs[:revision]
       end