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/bind/testdata/structs.go

Index: third_party/go/src/golang.org/x/mobile/bind/testdata/structs.go
diff --git a/third_party/go/src/golang.org/x/mobile/bind/testdata/structs.go b/third_party/go/src/golang.org/x/mobile/bind/testdata/structs.go
deleted file mode 100644
index 8dcabb75a82a9caec53c65097461f3bf77f79d81..0000000000000000000000000000000000000000
--- a/third_party/go/src/golang.org/x/mobile/bind/testdata/structs.go
+++ /dev/null
@@ -1,14 +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.
-
-package structs
-
-type S struct {
-	X, Y       float64
-	unexported bool
-}
-
-func (s *S) Sum() float64 {
-	return s.X + s.Y
-}