Clean QueryRecorder backtrace

This makes it much easier to debug N+1 queries via QueryRecorder by
eliminating unnecessary lines.

spec/support/helpers/query_recorder.rb

@@ -11,7 +11,7 @@ module ActiveRecord
 
     def show_backtrace(values)
       Rails.logger.debug("QueryRecorder SQL: #{values[:sql]}")
-      caller.each { |line| Rails.logger.debug("   --> #{line}") }
+      Gitlab::Profiler.clean_backtrace(caller).each { |line| Rails.logger.debug("   --> #{line}") }
     end
 
     def callback(name, start, finish, message_id, values)