Use the NavigationCollector from analyzer_plugin to avoid duplication

pkg/analysis_server/lib/plugin/analysis/navigation/navigation_core.dart

Index: pkg/analysis_server/lib/plugin/analysis/navigation/navigation_core.dart
diff --git a/pkg/analysis_server/lib/plugin/analysis/navigation/navigation_core.dart b/pkg/analysis_server/lib/plugin/analysis/navigation/navigation_core.dart
deleted file mode 100644
index 6e0cc40d67cfa0250ef62bfea262990e5479d02c..0000000000000000000000000000000000000000
--- a/pkg/analysis_server/lib/plugin/analysis/navigation/navigation_core.dart
+++ /dev/null
@@ -1,20 +0,0 @@
-// Copyright (c) 2015, 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.
-
-import 'package:analyzer_plugin/protocol/protocol_common.dart'
-    show ElementKind, Location;
-
-/**
- * An object used to record navigation regions.
- *
- * Clients may not extend, implement or mix-in this class.
- */
-abstract class NavigationCollector {
-  /**
-   * Record a new navigation region with the given [offset] and [length] that
-   * should navigate to the given [targetLocation].
-   */
-  void addRegion(
-      int offset, int length, ElementKind targetKind, Location targetLocation);
-}