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/example/libhellojni/hello.c

-// Copyright 2014 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// +build android
-
-// See main.go for commentary.
-
-#include <android/log.h>
-#include <jni.h>
-#include <limits.h>
-#include "_cgo_export.h"
-
-JNIEXPORT void JNICALL
-Java_demo_Demo_hello(JNIEnv* env, jclass clazz, jstring jname) {
-        // Turn Java's UTF16 string into (almost) UTF8.
-        const char *name = (*env)->GetStringUTFChars(env, jname, 0);
-
-        GoString go_name;
-        go_name.p = (char*)name;
-        go_name.n = (*env)->GetStringUTFLength(env, jname);
-
-        // Call into Go.
-        LogHello(go_name);
-
-        (*env)->ReleaseStringUTFChars(env, jname, name);
-}