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.go

-// 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
-
-package main
-
-// #cgo LDFLAGS: -llog
-// #include <android/log.h>
-// #include <string.h>
-import "C"
-import (
-        "fmt"
-        "unsafe"
-)
-
-//export LogHello
-func LogHello(name string) {
-        fmt.Printf("Hello, %s!\n", name)
-
-        ctag := C.CString("Go")
-        cstr := C.CString(fmt.Sprintf("Printing hello message for %q", name))
-        C.__android_log_write(C.ANDROID_LOG_INFO, ctag, cstr)
-        C.free(unsafe.Pointer(ctag))
-        C.free(unsafe.Pointer(cstr))
-}