Remove unnecessary condition to skip tag list test

This file only has tests related to tags; if the model doesn't have
tags, we simply wouldn't include `it_behaves_as` in their tests instead
of including it and then skipping it.

spec/shared/models/sanitizable.rb

@@ -2,12 +2,6 @@ shared_examples "sanitizable" do
   let(:sanitizable) { build(model_name(described_class)) }
 
   describe "#tag_list" do
-    before do
-      unless described_class.included_modules.include?(Taggable)
-        skip "#{described_class} does not have a tag list"
-      end
-    end
-
     it "sanitizes the tag list" do
       sanitizable.tag_list = "user_id=1"