Bluetooth: Delete Local JNI References

In android_server_BluetoothEventLoop.c and
android_server_BluetoothA2dpService functions, local
references to Java objects while running in the eventloop context
are not explicitly deleted when the functions return. Local
references are implicitly deleted by the JVM when JNI code returns.
However, in this implementation the eventloop code runs as a separate
native thread which is not called from the JVM, therefore any local
references created are not released by the JVM. To prevent memory
from being leaked and reference oveflow in the JVM, these local
references need to be explicitly released.

CRs-fixed: 211008 211226