Revert "Android: Generate JNI code for stats"

This reverts commit aede67a199ae0552074bfec4bb03cc9a6a5fba0f.

Reason for revert: Causes error:
JNI ERROR (app bug): local reference table overflow (max=512)'

Original change's description:
> Android: Generate JNI code for stats
> 
> This CL also unifies the functions for converting from C++ to Java, and
> generates the boiler plate for converting C++ vectors to Java arrays.
> 
> Bug: webrtc:8278
> Change-Id: I262e9162beae8a64ba0e8b6a27e1081207b03961
> Reviewed-on: https://webrtc-review.googlesource.com/26020
> Commit-Queue: Magnus Jedvert <magjed@webrtc.org>
> Reviewed-by: Sami Kalliomäki <sakal@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#20918}

TBR=magjed@webrtc.org,sakal@webrtc.org

Change-Id: Ieb26ed8577bd489a4dd4f7542d16a7d0e11f409f
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: webrtc:8278
Reviewed-on: https://webrtc-review.googlesource.com/26900
Reviewed-by: Magnus Jedvert <magjed@webrtc.org>
Commit-Queue: Magnus Jedvert <magjed@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20926}

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

@@ -13,5 +13,5 @@ package org.webrtc;
 /** Interface for observing Stats reports (see webrtc::StatsObservers). */
 public interface StatsObserver {
   /** Called when the reports are ready.*/
-  @CalledByNative public void onComplete(StatsReport[] reports);
+  public void onComplete(StatsReport[] reports);
 }