parse.y: remove unused argument

* parse.y (list_concat): remove unused argument parser, since
  never allocates new node.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47789 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* 2014-10-05

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47790 b2dd03c8-39d4-4d8f-98ff-823fe69b080e