remove useless conditional

we always have a response object, so there is no reason to test it

actionpack/lib/action_controller/metal/head.rb

@@ -45,7 +45,7 @@ def head(status, options = {})
 
       if include_content?(self.response_code)
         self.content_type = content_type || (Mime[formats.first] if formats)
-        self.response.charset = false if self.response
+        self.response.charset = false
       end
 
       true