Remove third_party/golang.org/x/mobile as it is no longer used with Go 1.5.

third_party/go/src/golang.org/x/mobile/app/Go.java

-package go;
-
-import android.content.Context;
-import android.os.Looper;
-import android.util.Log;
-
-// Go is an entry point for libraries compiled in Go.
-// In an app's Application.onCreate, call:
-//
-//      Go.init(getApplicationContext());
-//
-// When the function returns, it is safe to start calling
-// Go code.
-public final class Go {
-        // init loads libgojni.so and starts the runtime.
-        public static void init(final Context ctx) {
-                if (Looper.myLooper() != Looper.getMainLooper()) {
-                        Log.wtf("Go", "Go.init must be called from main thread (looper="+Looper.myLooper().toString()+")");
-                }
-                if (running) {
-                        return;
-                }
-                running = true;
-
-                // TODO(crawshaw): context.registerComponentCallbacks for runtime.GC
-
-                System.loadLibrary("gojni");
-
-                new Thread("GoMain") {
-                        public void run() {
-                                Go.run(ctx);
-                        }
-                }.start();
-
-                Go.waitForRun();
-
-        new Thread("GoReceive") {
-            public void run() { Seq.receive(); }
-        }.start();
-        }
-
-        private static boolean running = false;
-
-        private static native void run(Context ctx);
-        private static native void waitForRun();
-}