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

src/com/android/settings/bluetooth/BluetoothSettings.java

@@ -210,6 +210,7 @@ public final class BluetoothSettings extends DeviceListPreferenceFragment implem
     @Override
     public void onStop() {
         super.onStop();
+        mPairedDevicesCategory.removeAll();
         if (mBluetoothEnabler != null) {
             mBluetoothEnabler.pause();
         }