Revert "Make isBackDisabled() not SystemAPI"

This reverts commit f14fd636a1a9da39fa50d64296a1fe7e8ae5baba.

Reason for revert: The following bugs cite this Cl as the root issue: b/332752827 , b/325856557 , and b/332647161 

Change-Id: I4deed186801370d01828a1099d67c3c6bf75f1b8
2 files changed