Revert "Bring back CLEAN_EXPIRED_ASSETS environment variable."

This reverts commit 668f13b.

README.md

@@ -33,7 +33,7 @@ Enjoy your lightning fast deploys!
 
 ## Removing Expired Assets
 
-`turbo-sprockets-rails3` provides a Rake task called `assets:clean_expired`. You can run this task after `assets:precompile` to remove outdated assets. To automatically run this `assets:clean_expired` task after `assets:precompile`, you can set the `CLEAN_EXPIRED_ASSETS` environment variable to `true` (`CLEAN_EXPIRED_ASSETS=true rake assets:precompile`).
+`turbo-sprockets-rails3` provides a Rake task called `assets:clean_expired`. You can run this task after `assets:precompile` to remove outdated assets.
 
 If you use this rake task, you must set `config.assets.handle_expiration` to true in `config/environments/production.rb`. This makes sure that asset modification times
 are updated properly before `assets:precompile`, so that the `clean_expired` task knows which assets are safe to remove.

lib/turbo-sprockets/tasks/assets.rake

@@ -202,8 +202,3 @@ task_enhancements.each do |task_name, actions|
     Rake::Task[task_name].enhance &proc
   end
 end
-
-# Clean expired assets after asset precompile, if CLEAN_EXPIRED_ASSETS is set
-Rake::Task["assets:precompile:all"].enhance do
-  Rake::Task["assets:clean_expired:all"].invoke if ENV['CLEAN_EXPIRED_ASSETS'].in? %w(true yes 1)
-end