Remove DartPackage annotation from NativeViewport and GPU mojoms

mojo/services/gpu/interfaces/context_provider.mojom

 // 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.
 
-[DartPackage="mojo_services"]
 module mojo;
 
 import "gpu/interfaces/command_buffer.mojom";
 import "gpu/interfaces/viewport_parameter_listener.mojom";
 
 // A ContextProvider can be used to provide new command buffers related to a
 // particular context, for instance configured to draw to a particular display.
 interface ContextProvider {
   // This initializes a new command buffer for this provider when available,
   // closing connections to the previously created command buffer (if any).
   //
   // This call may not return for an extended period of time if a command
   // buffer cannot be produced immediately, for example if it is associated
   // with a view that is offscreen.
   //
   // If a viewport_parameter_listener is provided it will notified be when
   // vsync parameters change for this context.
   //
   // The returned handle will be null if no command buffer can be created for
   // this request, for example if another request is made on the same provider
   // before a previous call returns.
   Create(ViewportParameterListener? viewport_parameter_listener)
       => (CommandBuffer? gles2_client);
 };