hash.c (rb_any_hash): remove unnecessary dsym check

gcc (Debian 4.7.2-5) 4.7.2 on x86 generates smaller code this
way, as it does not seem to be able to reuse the result of
SPECIAL_CONST_P.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47853 b2dd03c8-39d4-4d8f-98ff-823fe69b080e