Combine webrtc/api/java/android and webrtc/api/java/src.

It used to be that there was a Java api for devices not running Android
but that is no longer the case. I combined the directories and made
the folder structure chromium style.

BUG=webrtc:6067
R=magjed@webrtc.org, tommi@webrtc.org

Review URL: https://codereview.webrtc.org/2111823002 .

Cr-Commit-Position: refs/heads/master@{#13356}

webrtc/api/test/androidtestinitializer.cc

@@ -19,8 +19,8 @@
 #include "base/android/context_utils.h"
 #include "base/android/jni_android.h"
 
-#include "webrtc/api/java/jni/classreferenceholder.h"
-#include "webrtc/api/java/jni/jni_helpers.h"
+#include "webrtc/api/android/jni/classreferenceholder.h"
+#include "webrtc/api/android/jni/jni_helpers.h"
 #include "webrtc/base/checks.h"
 #include "webrtc/base/ssladapter.h"
 #include "webrtc/voice_engine/include/voe_base.h"