Revert "Also delegates the message message."

This reverts commit 2885db5.

This needs more careful consideration since it would break anyone using
`let(:message)`. See rspec#152 for more details.

lib/rspec/rails/adapters.rb

@@ -47,7 +47,7 @@ module ClassMethods
         # Minitest.
         def assertion_method_names
           Test::Unit::Assertions.public_instance_methods.select{|m| m.to_s =~ /^(assert|flunk)/} +
-            [:build_message, :message]
+            [:build_message]
         end
 
         # @api private