backup: mark 'encryption' option as deprecated - all backups are encrypted
backup: mark 'encryption' option as deprecated - all backups are encrypted

QubesOS/qubes-issues#971

woju/qubes-core-admin,QubesOS/qubes-core-admin,woju/qubes-core-admin,marmarek/qubes-core-admin,woju/qubes-core-admin,marmarek/qubes-core-admin,QubesOS/qubes-core-admin,QubesOS/qubes-core-admin,marmarek/qubes-core-admin,woju/qubes-core-admin