load.c: no longer used variable and object

* load.c (rb_feature_p): remvoe variable and string object which are
  no longer used since r39874.  [Bug #8048]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39898 b2dd03c8-39d4-4d8f-98ff-823fe69b080e