Remove invalidating ConfigStore in onDestroy.

This is causing NPE for cases where `state.configStore`, being
retrieved from `savedInstance` is null. The ConfigStore object was being
nullified in onDestroy because earlier it was using device config flag
which needed to updated in new sessions.

Bug: 348384263
Bug: 348384263
Bug: 335553196
Test: Manually
Flag: EXEMPT bugfix
Change-Id: I6687bee4aef1f73d21a08cfd433c636082148621