recovery: remove checks for system wipe on SAR devices

* SAR devices apparently has a mount point set to "/" and is detected
the same which apparently breaks the comparison when formatting "/system".

* ensure_path_unmounted also breaks due to the mount point being set as
"/" and rootfs can never be unmounted.

Temporary workaround until a better solution is found.

Also, remove "Mount system" option for SAR devices so that no one
accidently mount it before a wipe and have troubles unmounting it.

Signed-off-by: Sumit Pundir <pundir.sumit@e.email>