+ Removed RubyParserExtras#arg_add. (presidentbeef! YAY!)
+ Cleaned up and re-ordered node_assign to be faster (ordered by actual occurrance).

[git-p4: depot-paths = "//src/ruby_parser/dev/": change = 9185]
+ Removed :call case of node_assign. I don't think it is possible.

[git-p4: depot-paths = "//src/ruby_parser/dev/": change = 9186]