cask --cache: Remove deprecation comment

Library/Homebrew/cask/cmd/--cache.rb

@@ -18,9 +18,6 @@ module Cask
       end
 
       def run
-        # TODO: enable for next major/minor release
-        # odeprecated "brew cask --cache", "brew --cache --cask"
-
         casks.each do |cask|
           puts self.class.cached_location(cask)
         end