remount: Don't assert ro.boot.vbmeta.* properties

ro.boot.vbmeta.* properties could be missing if device is verification
disabled.
Instead use ro.boot.verifiedbootstate to check device locked state.
No need to check ro.boot.vbmeta.digest, as we no longer support VB1.0.
In other words, all device running this piece of code must be using AVB.

Bug: 241688845
Test: adb-remount-test
Change-Id: If5d702ab3a6f12deef8204dba698e6c62eaae46f