message: minor code cleanup in swagger validation rule file
diff: // Licensed under the MIT License. See License.txt in the project root for license information.
  using AutoRest.Core.Logging;
  -using AutoRest.Core.Validation;
  -using AutoRest.Swagger.Model;
  -using System.Collections.Generic;
  namespace AutoRest.Swagger.Validation
  {
  @@ -12,17 +9,6 @@ namespace AutoRest.Swagger.Validation
  {
  protected override string ExtensionName => "x-ms-mutability";
  - protected static Schema Get200ResponseSchema(RuleContext context)
  - {
  - OperationResponse response = context?.GetFirstAncestor<Operation>()?.Responses?.GetValueOrNull("200");
  - if (response == null)
  - {
  - return null;
  - }
  - var resolver = new SchemaResolver(context?.GetServiceDefinition());
  - return resolver.Unwrap(response.Schema);
  - }
  -
  public abstract override string MessageTemplate { get; }
  /// <summary>
  