Fix 'Unused local variable' hints in analyzer and analysis_server.

pkg/analysis_server/test/services/index/dart_index_contributor_test.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 test.services.src.index.dart_index_contributor;
 
 import 'package:analysis_server/src/services/index/index.dart';
 import 'package:analysis_server/src/services/index/index_contributor.dart';
 import 'package:analysis_server/src/services/index/index_store.dart';
 import 'package:analyzer/src/generated/ast.dart';
@@ skipping 114 matching lines @@
   void test_NameElement_isDefinedBy_localVariable_inForEach() {
     _indexTestUnit('''
 class A {
   main() {
     for (int test in []) {
     }
   }
 }
 ''');
     // prepare elements
-    Element mainElement = findElement('main');
     LocalVariableElement testElement = findElement('test');
     Element nameElement = new NameElement('test');
     // verify
     _assertRecordedRelation(
         nameElement,
         IndexConstants.NAME_IS_DEFINED_BY,
         _expectedLocation(testElement, 'test in []'));
   }
 
   void test_NameElement_method() {
@@ skipping 1609 matching lines @@
 
   RecordedRelation(this.element, this.relationship, this.location);
 
   @override
   String toString() {
     return 'RecordedRelation(element=$element; relationship=$relationship; '
         'location=$location; flags=' '${location.isQualified ? "Q" : ""}'
         '${location.isResolved ? "R" : ""})';
   }
 }