Fix phone's UI shows incorrect status by releasing message in handler

Root Cause: switchSubDeviceContent() but mHandler did not be cleared and might execute the delay message from another device.

Solution: Remember to release mHandler object when target is changed or removed.

Bug: 237457702
Test: make RunSettingsLibRoboTests ROBOTEST_FILTER=CachedBluetoothDeviceTest
Change-Id: I05f3c948758fbca8627eec8dc32e32cbdd80b763
3 files changed