array.c: use rb_hash_values

* array.c (rb_ary_uniq): use rb_hash_values(), as well as the case no
  block is given.
* internal.h: define rb_hash_values() as internal API.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43197 b2dd03c8-39d4-4d8f-98ff-823fe69b080e