DO NOT MERGE Fix JNI global references leak in AudioEffect

Added deletion of global references in native AudioEffect
implementation to avoid reaching maximum number of global references.

Issue can be reproduced with the following code snippet:

AudioTrack track = new AudioTrack(...);
BassBoost effect;
while(true) {
    effect = new BassBoost(0, track.getAudioSessionId());
    effect.release();
    effect = null;
}

Crash will happen after a few seconds when system runs out of
global references.

Change-Id: I3343967aae60784e61279e26151a28d01457c78b