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/audio/audio_test.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.
-
-// +build darwin
-
-package audio
-
-import (
-        "testing"
-        "time"
-)
-
-func TestNoOp(t *testing.T) {
-        var p *Player
-        if err := p.Play(); err != nil {
-                t.Errorf("no-op player failed to play: %v", err)
-        }
-        if err := p.Pause(); err != nil {
-                t.Errorf("no-op player failed to pause: %v", err)
-        }
-        if err := p.Stop(); err != nil {
-                t.Errorf("no-op player failed to stop: %v", err)
-        }
-        if c := p.Current(); c != time.Duration(0) {
-                t.Errorf("no-op player returns a non-zero playback position: %v", c)
-        }
-        if tot := p.Total(); tot != time.Duration(0) {
-                t.Errorf("no-op player returns a non-zero total: %v", tot)
-        }
-        if vol := p.Volume(); vol != 0 {
-                t.Errorf("no-op player returns a non-zero total: %v", vol)
-        }
-        if s := p.State(); s != Unknown {
-                t.Errorf("playing state: %v", s)
-        }
-        p.SetVolume(0.1)
-        p.Seek(time.Duration(100))
-        p.Destroy()
-}