parse.y: unused return values

* parse.y (arg_var_gen, local_var_gen): make void since the result
  values are not used.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45844 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
parse.y: remove duplicated names

* parse.y (local_tbl_gen): remove local variables duplicated with
  arguments.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45845 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
parse.y: no duplicated names

* parse.y (new_bv_gen): no duplicated names, if already added in
  shadowing_lvar().

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45846 b2dd03c8-39d4-4d8f-98ff-823fe69b080e