[rubygems/rubygems] Remove out of date TODO

After digging into git history a bit, I figure this was about unifying
`bundle cache` and `bundle package`, which already happened a while ago.
So remove this TODO since it's now misleading.

5a0b06b84d

lib/bundler/cli/cache.rb

@@ -16,7 +16,6 @@ module Bundler
       setup_cache_all
       install
 
-      # TODO: move cache contents here now that all bundles are locked
       custom_path = Bundler.settings[:path] if options[:path]
 
       Bundler.settings.temporary(cache_all_platforms: options["all-platforms"]) do