Revert of [builtins] DeleteProperty: Handle last-added fast properties

src/compiler/js-native-context-specialization.cc

Index: src/compiler/js-native-context-specialization.cc
diff --git a/src/compiler/js-native-context-specialization.cc b/src/compiler/js-native-context-specialization.cc
index 661b025d0acc3d822e3ac1a07d6956c9a6c594ea..88d0fba216e0d8f1ab5febcbd98fccec476b534b 100644
--- a/src/compiler/js-native-context-specialization.cc
+++ b/src/compiler/js-native-context-specialization.cc
@@ -2310,15 +2310,6 @@
 
 Node* JSNativeContextSpecialization::BuildExtendPropertiesBackingStore(
     Handle<Map> map, Node* properties, Node* effect, Node* control) {
-  // TODO(bmeurer/jkummerow): Property deletions can undo map transitions
-  // while keeping the backing store around, meaning that even though the
-  // map might believe that objects have no unused property fields, there
-  // might actually be some. It would be nice to not create a new backing
-  // store in that case (i.e. when properties->length() >= new_length).
-  // However, introducing branches and Phi nodes here would make it more
-  // difficult for escape analysis to get rid of the backing stores used
-  // for intermediate states of chains of property additions. That makes
-  // it unclear what the best approach is here.
   DCHECK_EQ(0, map->unused_property_fields());
   // Compute the length of the old {properties} and the new properties.
   int length = map->NextFreePropertyIndex() - map->GetInObjectProperties();