Remove outdated TODO in RemoteFetcher

Author: afurm

lib/rubygems/remote_fetcher.rb

@@ -173,7 +173,7 @@ def download(spec, source_uri, install_dir = Gem.dir)
       end
 
       verbose "Using local gem #{local_gem_path}"
-    when nil then # TODO: test for local overriding cache
+    when nil then
       source_path = if Gem.win_platform? && source_uri.scheme &&
                        !source_uri.path.include?(":")
         "#{source_uri.scheme}:#{source_uri.path}"