add UNKNOWN_SOURCE error code and remove 2 unused legacy error codes

pkg/analysis_server/test/integration/protocol_matchers.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. 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 has been automatically generated.  Please do not edit it manually.
 // To regenerate the file, use the script
 // "pkg/analysis_server/tool/spec/generate_files".
 
 /**
  * Matchers for data types defined in the analysis server API
@@ skipping 1815 matching lines @@
  *   INVALID_PARAMETER
  *   INVALID_REQUEST
  *   NO_INDEX_GENERATED
  *   REFACTORING_REQUEST_CANCELLED
  *   SERVER_ALREADY_STARTED
  *   SERVER_ERROR
  *   SORT_MEMBERS_INVALID_FILE
  *   SORT_MEMBERS_PARSE_ERRORS
  *   UNANALYZED_PRIORITY_FILES
  *   UNKNOWN_REQUEST
+ *   UNKNOWN_SOURCE
  *   UNSUPPORTED_FEATURE
  * }
  */
 final Matcher isRequestErrorCode = new MatchesEnum("RequestErrorCode", [
   "CONTENT_MODIFIED",
   "FORMAT_INVALID_FILE",
   "GET_ERRORS_INVALID_FILE",
   "INVALID_EXECUTION_CONTEXT",
   "INVALID_OVERLAY_CHANGE",
   "INVALID_PARAMETER",
   "INVALID_REQUEST",
   "NO_INDEX_GENERATED",
   "REFACTORING_REQUEST_CANCELLED",
   "SERVER_ALREADY_STARTED",
   "SERVER_ERROR",
   "SORT_MEMBERS_INVALID_FILE",
   "SORT_MEMBERS_PARSE_ERRORS",
   "UNANALYZED_PRIORITY_FILES",
   "UNKNOWN_REQUEST",
+  "UNKNOWN_SOURCE",
   "UNSUPPORTED_FEATURE"
 ]);
 
 /**
  * SearchId
  *
  * String
  */
 final Matcher isSearchId = isString;
 
@@ skipping 314 matching lines @@
  *
  * {
  *   "newName": String
  * }
  */
 final Matcher isRenameOptions = new LazyMatcher(() => new MatchesJsonObject(
   "rename options", {
     "newName": isString
   }));