Make depending on a specific audio implementation optional.

Splits out audio_java into audio_api_java and
java_audio_device_module_java.

Makes depending on java_audio_device_module_jni optional for clients
that do not use it. It is only necessary to depend on this target if
depending on java_audio_device_module_java.

Also some cleanup.

Bug: webrtc:7452
Change-Id: Ic6c4dbe11db3ed8330802a8e90203acb8ef18e72
Reviewed-on: https://webrtc-review.googlesource.com/70220
Commit-Queue: Sami Kalliomäki <sakal@webrtc.org>
Reviewed-by: Magnus Jedvert <magjed@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22981}

sdk/android/api/org/webrtc/audio/LegacyAudioDeviceModule.java

@@ -21,10 +21,6 @@ import org.webrtc.voiceengine.WebRtcAudioTrack;
  */
 @Deprecated
 public class LegacyAudioDeviceModule implements AudioDeviceModule {
-  public static AudioDeviceModule Create() {
-    return new LegacyAudioDeviceModule();
-  }
-
   @Override
   public long getNativeAudioDeviceModulePointer() {
     // Returning a null pointer will make WebRTC construct the built-in legacy AudioDeviceModule for