Refined the following parts:
- Remove ConnectA2dpTask/DisconnectA2dpTask and call Connect/Disconnect directly in BluetoothHfpManager
- Remove BroadcastSystemMessage(const nsAString& aType)
- Replace SetupA2dpDevice & TeardownA2dpDevice with NotifyAudioManager
Merge pull request #1 from ginayeh/TestA2dpAvrcp13

Refined the following parts: