no need to clear an unusued collection

If the code reaches that line new_constants is no longer needed.
We only need here to iterate over it to discard stuff and done.

Note that constant_watch_stack.new_constants returns a new
reference each time it is invoked, so that #clear call was not
cleaning state in some internal structure (which would have been
a bit dirty as well at this level of coupling).

activesupport/lib/active_support/dependencies.rb

@@ -666,7 +666,7 @@ module ActiveSupport #:nodoc:
 
         return new_constants unless aborting
 
-        new_constants.each { |c| remove_constant(c) }.clear
+        new_constants.each { |c| remove_constant(c) }
       end
     end