Revert "Implement ES6 symbol registry and predefined symbols"

src/heap.h

Index: src/heap.h
diff --git a/src/heap.h b/src/heap.h
index 0446a988d73d90af7b05732ae44fa74381ffdaee..4c280aa8f474159624898567c78b50868b818704 100644
--- a/src/heap.h
+++ b/src/heap.h
@@ -190,7 +190,6 @@ namespace internal {
   V(Cell, undefined_cell, UndefineCell)                                        \
   V(JSObject, observation_state, ObservationState)                             \
   V(Map, external_map, ExternalMap)                                            \
-  V(JSObject, symbol_registry, SymbolRegistry)                                 \
   V(Symbol, frozen_symbol, FrozenSymbol)                                       \
   V(Symbol, nonexistent_symbol, NonExistentSymbol)                             \
   V(Symbol, elements_transition_symbol, ElementsTransitionSymbol)              \