Revert certbackup

Fix https://gitlab.labs.nic.cz/turris/turris-os-packages/issues/467

Certificate backup restore is handled by hook run by schnapps so this code duplicates that functionality. It should not be there.

It is also wrong as some of the files are hidden (starting with dot) and this copy omits them. At the same time it prints error if there is no file in store (this is "fixed" by hiding errors but nooo).

On notice @mhrusecky I am planning on tagging this as 2.2.1 version of schnapps.