remove wrong expectation

* spec/rubyspec/core/kernel/itself_spec.rb: `object_id` may return
  different objects for each calls, and the expectation of object
  identity is done by `equal` matcher which uses `equal?` method.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58704 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

spec/rubyspec/core/kernel/itself_spec.rb

@@ -5,6 +5,5 @@ describe "Kernel#itself" do
   it "returns the receiver itself" do
     foo = Object.new
     foo.itself.should equal foo
-    foo.itself.object_id.should equal foo.object_id
   end
 end