Android JNI generation: Set JNI namespace in build files

This CL removes the use of the @JNINamespace annotation and instead
sets the correct JNI namespace in the build file.

Bug: webrtc:8278
Change-Id: Ia4490399e45a97d56b02c260fd80df4edfa092bf
Reviewed-on: https://webrtc-review.googlesource.com/76440
Commit-Queue: Magnus Jedvert <magjed@webrtc.org>
Reviewed-by: Sami Kalliomäki <sakal@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23299}

sdk/android/api/org/webrtc/VideoFileRenderer.java

@@ -24,7 +24,6 @@ import java.util.concurrent.LinkedBlockingQueue;
 /**
  * Can be used to save the video frames to file.
  */
-@JNINamespace("webrtc::jni")
 public class VideoFileRenderer implements VideoSink {
   private static final String TAG = "VideoFileRenderer";