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/cmd/gomobile/install.go

-// Copyright 2015 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.
-
-package main
-
-import (
-        "os"
-        "os/exec"
-        "path/filepath"
-)
-
-var cmdInstall = &command{
-        run:   runInstall,
-        Name:  "install",
-        Usage: "[package]",
-        Short: "compile android APK and/or iOS app and install on device",
-        Long: `
-Install compiles and installs the app named by the import path on the
-attached mobile device.
-
-This command requires the 'adb' tool on the PATH.
-
-See the build command help for common flags and common behavior.
-`,
-}
-
-func runInstall(cmd *command) error {
-        if err := runBuild(cmd); err != nil {
-                return err
-        }
-        install := exec.Command(
-                `adb`,
-                `install`,
-                `-r`,
-                filepath.Base(pkg.Dir)+`.apk`,
-        )
-        if buildV {
-                install.Stdout = os.Stdout
-                install.Stderr = os.Stderr
-        }
-        return install.Run()
-}