Remove deprecation on calling assert_equal with nil

Author: rafaelfranca

railties/test/application/backtrace_cleaner_test.rb

@@ -39,7 +39,7 @@ class BacktraceCleanerTest < ActiveSupport::TestCase
 
       cleaned = @cleaner.clean_frame(frame)
 
-      assert_equal nil, cleaned
+      assert_nil cleaned
     end
 
     test "#clean_frame does not silence when BACKTRACE is set" do