Revert^2 "init: Look for super partition only on a boot device"

This reverts commit 8d71220df28851a7dce351f86601958fdbc3e5ae.

Reason for revert: Fix for gcar emulator (basically all QEMU-based emulators) landed at aosp/3315253 and aosp/3160116.

Change-Id: If4eddd3f7e224c31019ad3bd752e2375c7567780
3 files changed