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/java/README

@@ -1,10 +0,0 @@
-This directory holds a Java implementation of the webrtc::PeerConnection API, as
-well as the JNI glue C++ code that lets the Java implementation reuse the C++
-implementation of the same API.
-
-To build the Java API and related tests, build with OS=android in $GYP_DEFINES.
-
-To use the Java API, start by looking at the public interface of
-org.webrtc.PeerConnection{,Factory} and the org.webrtc.PeerConnectionTest.
-
-To understand the implementation of the API, see the native code in jni/.