When deregister bta_sys_deregister set nullptr am: 5922eec9 am: f3e3385a am: f0c5d279

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



Change-Id: Ib92c8d80875334ead2261b88fb549e7b3f0bb21c
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>