[#64241148] fixup smokey

This fixes something that I didn't spot in https://github.com/alphagov/smokey/pull/64 which is that the new step had been added to frontend_steps.rb but not removed from whitehall_steps.rb

I've also marked them as Pending, which stops them running via Icinga. That's because:
1) They are not actually checking the mirror, because we've not set the host to point to the mirror
2) You can't contact the mirror from anything other than Production, so the check won't work in Preview.

I've got [some idea how to check the mirror directly](https://github.com/alphagov/smokey/compare/64241148-check-the-mirrors), but it's going to take some firewall fiddling to work in Preview and Staging and I'm not sure how we want to handle that - it may be better to tag these checks with @mirror and then only run them in smokey in Production.