When deregister bta_sys_deregister set nullptr am: 5922eec9 am: f3e3385a

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Bluetooth/+/2056574



Change-Id: I9716f1710485767a10617e0d37795d50f9b19b00
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>