Replace Linked{Identity,Custom}Hash{Map,Set} with compact implementation; remove old code and flag.

runtime/lib/linked_hash_map.cc

Index: runtime/lib/linked_hash_map.cc
===================================================================
--- runtime/lib/linked_hash_map.cc	(revision 44194)
+++ runtime/lib/linked_hash_map.cc	(working copy)
@@ -14,8 +14,8 @@
 namespace dart {
 
 DEFINE_FLAG(bool, use_internal_hash_map, false, "Use internal hash map.");
-DEFINE_FLAG(bool, use_compact_hash, true, "Use compact hash map and set.");
 
+
 DEFINE_NATIVE_ENTRY(LinkedHashMap_allocate, 1) {
   const TypeArguments& type_arguments =
       TypeArguments::CheckedHandle(arguments->NativeArgAt(0));
@@ -91,14 +91,7 @@
 
 
 DEFINE_NATIVE_ENTRY(LinkedHashMap_useInternal, 0) {
-  ASSERT(!(FLAG_use_internal_hash_map && FLAG_use_compact_hash));
   return Bool::Get(FLAG_use_internal_hash_map).raw();
 }
 
-
-DEFINE_NATIVE_ENTRY(LinkedHashMap_useCompact, 0) {
-  ASSERT(!(FLAG_use_internal_hash_map && FLAG_use_compact_hash));
-  return Bool::Get(FLAG_use_compact_hash).raw();
-}
-
 }  // namespace dart