Dont call close in in BluetoothA2dp finalize

The close in finalize() is pointless, as finalize() will only be called
if there are no references to BluetoothA2dp. Until close() is called,
BluetoothManagerService will have a reference to BluetoothA2dp,
preventing garbage collection and finalize() to be called. This means
finalize() is not serving its purpose of cleaning up in cases close()
is not called, as finalize() is only called if close() has already
been called.

Actually calling close in finalize here means unregistering the already
unregistered mBluetoothStateChangeCallback which can lead to crashes
when pairing/unpairing BTH. A typical crash would look like:

*** FATAL EXCEPTION IN SYSTEM PROCESS: BluetoothManager
java.lang.NullPointerException
at android.os.RemoteCallbackList.unregister(RemoteCallbackList.java:143)
at com.android.server.BluetoothManagerService$BluetoothHandler.handleMessage(BluetoothManagerService.java:780)
at android.os.Handler.dispatchMessage(Handler.java:99)

Change-Id: Ib65962917ecbacf7900d7fe540057e6915f0532d