init: call umount unconditionally

std::all_of is using std::find_if, which means, if any element the given
predicate returns false, it stops further iteration and just returns false.
std::all_of used in Reboot.cpp will cause umount not to be called on all
block devices if some block device returns false in the middle.

Bug: 68158923
Test: reboot
Change-Id: I43ba6bd0c18018c1ed5fe2b63996552bc51cc67c