Fix verify_root_and_recovery menu selections

Because of the way default_recovery_keys.c is setup, hiding the back
button causes the POWER and SEARCH keys to no longer work as selection
keys.
- Remove old legacy unused code
- Keep the device_reboot_now API if one needs to use it
- Hide the Go Back button from confirm menu
Change-Id: I517690a7b9f85ccc778f2bb6acbf967c1416d1fc