Clean atom-shell caches in 'rake clean'.

Rakefile

@@ -73,15 +73,11 @@ task :clean do
   `rm -rf #{application_path()}`
   `rm -rf #{BUILD_DIR}`
   `rm -rf /tmp/atom-coffee-cache`
+  `rm -rf /tmp/atom-cached-atom-shells`
   `rm -rf node_modules`
   `rm -rf atom-shell`
 end
 
-desc "Delete cached atom-shells"
-task "clean-atom-shell-cache" do
-  `rm -rf /tmp/atom-cached-atom-shells`
-end
-
 desc "Run the specs"
 task :test => ["clone-default-bundles", "build"] do
   `pkill Atom`