Remove unused 'receiver' field from generators

src/debug/mirrors.js

Index: src/debug/mirrors.js
diff --git a/src/debug/mirrors.js b/src/debug/mirrors.js
index a2777abc1ffd153ca2519f91f533603505e9deb0..3f39f4a2cafdd9e1d071272af180e3a5e22cd7ae 100644
--- a/src/debug/mirrors.js
+++ b/src/debug/mirrors.js
@@ -1443,14 +1443,6 @@ GeneratorMirror.prototype.func = function() {
 };
 
 
-GeneratorMirror.prototype.receiver = function() {
-  if (!this.receiver_) {
-    this.receiver_ = MakeMirror(%GeneratorGetReceiver(this.value_));
-  }
-  return this.receiver_;
-};
-
-
 /**
  * Base mirror object for properties.
  * @param {ObjectMirror} mirror The mirror object having this property
@@ -2779,7 +2771,6 @@ JSONProtocolSerializer.prototype.serializeObject_ = function(mirror, content,
     content.status = mirror.status();
 
     content.func = this.serializeReference(mirror.func())
-    content.receiver = this.serializeReference(mirror.receiver())
 
     // If the generator is suspended, the content add line/column properties.
     serializeLocationFields(mirror.sourceLocation(), content);