Get rid of extra local var that does not add to the logic

There are too many "action name" variables around the process method.

actionpack/lib/abstract_controller/base.rb

@@ -125,9 +125,9 @@ def method_added(name)
     # ==== Returns
     # * <tt>self</tt>
     def process(action, *args)
-      @_action_name = action_name = action.to_s
+      @_action_name = action.to_s
 
-      unless action_name = method_for_action(action_name)
+      unless action_name = method_for_action(@_action_name)
         raise ActionNotFound, "The action '#{action}' could not be found for #{self.class.name}"
       end