parse.y: fix wrong static symbol

* parse.y (next_id): no reason to set ID_STATIC_SYM here, as ID
  returned by rb_intern3 can be a dynamic symbol and the static
  symbol flag is set otherwise.  [Bug #9787]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45788 b2dd03c8-39d4-4d8f-98ff-823fe69b080e