Revert "init: Look for super partition only on a boot device"

This reverts commit 6f0ebcb5260a8e769e0e029596d21c0efabe361b.

Reason for revert: b/371393845 boot up failure of gcar emulator

Change-Id: I15e5bea609938cf5a1e347666b9a2abb287cb086
3 files changed