Fix memory leak in Bluetooth settings

Bluetooth settings screen has two categories. Each category should call
removeAll() method to unregister a callback from CachedBluetoothDevice.
But the method is not called for mPairedDevicesCategory.

Bug: 30004142
Test: manual - connect to Bluetooth device and then
               open and close Bluetooth settings screen repeatedly

Change-Id: I5a72994473ee2bb5fc3ad00176d9a930b4839099