go/bindings: update code to pass structs versions tests

mojo/public/tools/bindings/generators/go_templates/source.tmpl

 // Copyright 2015 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.
 
 // This file is autogenerated by:
 //     mojo/public/tools/bindings/mojom_bindings_generator.py
 // For:
 //     {{module.path}}
 //
 
 package {{package}}
 
 import (
-        "fmt"
         "mojo/public/go/system"
 {% for i in imports %}
         {{i}}
 {% endfor %}
 )
 
-var _ = fmt.Errorf
 var _ = system.GetCore
 
 {% import "enum.tmpl" as enum_macros %}
 {% import "interface.tmpl" as interface_macros %}
 {% import "struct.tmpl" as struct_macros %}
 
 {#- Enum definitions #}
 {% for enum in enums %}
 {{enum_macros.define(enum)}}
 {%- endfor %}
 
 {#- Interface definitions #}
 {% for interface in interfaces %}
 {{interface_macros.define(interface)}}
 {%- endfor %}
 
 {#- Struct definitions #}
 {% for struct in structs %}
 {{struct_macros.define(struct)}}
 {%- endfor %}