Remove BluetoothEventManager#setReceiverHandler

Make BluetoothEventManager fields final and remove the method to
unregister receivers unnecessarily (introduced in b/35415158).

Bug: 113122466
Test: runtest systemui && make RunSettingsLibRoboTests
Change-Id: I8f34ab1a809638959ab4096a829c72b3d1ac3a23
7 files changed