Remove BuilderContext from summary builders.

pkg/analyzer/lib/src/summary/base.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.
 
 /**
  * Base functionality which code generated summary classes are built upon.
  */
 library analyzer.src.summary.base;
 
 /**
- * Instances of this class encapsulate the necessary state to keep track of a
- * serialized summary that is in the process of being built.
- *
- * This class is intended to be passed to the constructors of the summary
- * Builder classes.
- */
-class BuilderContext {
-  // Note: at the moment this is a placeholder class since the current
-  // serialization format (JSON) doesn't require any state tracking.  If/when
-  // we switch to a serialization format that requires state tracking, the
-  // state will be stored here.
-}
-
-/**
  * Instances of this class represent data that has been read from a summary.
  */
 abstract class SummaryClass {
   /**
    * Translate the data in this class into a map whose keys are the names of
    * fields and whose values are the data stored in those fields.
    *
    * Intended for testing and debugging only.
    */
   Map<String, Object> toMap();
 }