[New go generator] Implement declaring unions.

mojom/generators/go/templates/declarations.go

Index: mojom/generators/go/templates/declarations.go
diff --git a/mojom/generators/go/templates/declarations.go b/mojom/generators/go/templates/declarations.go
deleted file mode 100644
index c16bdc4b3a121c54274a5b52d16ad55fc37e0b3f..0000000000000000000000000000000000000000
--- a/mojom/generators/go/templates/declarations.go
+++ /dev/null
@@ -1,16 +0,0 @@
-// Copyright 2016 The Chromium 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 templates
-
-const structDeclTmplText = `
-{{- define "StructDecl" -}}
-{{$struct := . -}}
-type {{$struct.Name}} struct {
-{{- range $field := $struct.Fields}}
-	{{$field.Name}} {{$field.Type}}
-{{- end}}
-}
-{{- end -}}
-`