Reduction of writes into NVRAM

It's not a good idea to delete and then recreate back most of UEFI boot options during update.

So, the update algorithm was changed to more reasonable: it removes only outdated boot options and creates only new boot options.
It allows dramatically decrease the number of writes to NVRAM and even avoid write in case when nothing changed.

The same time this technique have some disadvantage: you can't overwrite boot options that was created with some mistakes. First You have to delete them manually (efibootmgr -Bb) and then start uefiboot-update.