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/desktop.go

Index: third_party/go/src/golang.org/x/mobile/app/desktop.go
diff --git a/third_party/go/src/golang.org/x/mobile/app/desktop.go b/third_party/go/src/golang.org/x/mobile/app/desktop.go
deleted file mode 100644
index 12434b2bc2941f6a14db8b13334727f48bb8d9f2..0000000000000000000000000000000000000000
--- a/third_party/go/src/golang.org/x/mobile/app/desktop.go
+++ /dev/null
@@ -1,25 +0,0 @@
-// 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 linux,!android darwin
-
-package app
-
-import (
-	"os"
-	"path/filepath"
-)
-
-// Logic shared by desktop debugging implementations.
-
-func openAsset(name string) (ReadSeekCloser, error) {
-	if !filepath.IsAbs(name) {
-		name = filepath.Join("assets", name)
-	}
-	f, err := os.Open(name)
-	if err != nil {
-		return nil, err
-	}
-	return f, nil
-}