Remove deprecated code

pkg/analysis_server/test/mocks.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.
 
 library mocks;
 
 import 'dart:async';
 import 'dart:io';
 @MirrorsUsed(targets: 'mocks', override: '*')
 import 'dart:mirrors';
@@ skipping 101 matching lines @@
   final ElementKind kind = ElementKind.FUNCTION;
   noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
 }
 
 class MockFunctionTypeAliasElement extends TypedMock
     implements FunctionTypeAliasElement {
   final ElementKind kind = ElementKind.FUNCTION_TYPE_ALIAS;
   noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
 }
 
-class MockHtmlElement extends TypedMock implements HtmlElement {
-  final ElementKind kind = ElementKind.HTML;
-  noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
-}
-
 class MockImportElement extends TypedMock implements ImportElement {
   final ElementKind kind = ElementKind.IMPORT;
   noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
 }
 
 class MockLibraryElement extends TypedMock implements LibraryElement {
   final ElementKind kind = ElementKind.LIBRARY;
   noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
 }
 
@@ skipping 325 matching lines @@
     }
     return mismatchDescription;
   }
 
   @override
   bool matches(item, Map matchState) {
     Response response = item;
     return response != null && response.id == _id && response.error == null;
   }
 }