Enable ES6 Map and Set by default

src/flag-definitions.h

Index: src/flag-definitions.h
diff --git a/src/flag-definitions.h b/src/flag-definitions.h
index 19a04e45cf65c8469b6ba2ed7a26d2c044af1f76..9ea8d1c49c930fab24106a4d6069ca3fa6665b4c 100644
--- a/src/flag-definitions.h
+++ b/src/flag-definitions.h
@@ -154,8 +154,6 @@ DEFINE_BOOL(harmony_scoping, false, "enable harmony block scoping")
 DEFINE_BOOL(harmony_modules, false,
             "enable harmony modules (implies block scoping)")
 DEFINE_BOOL(harmony_proxies, false, "enable harmony proxies")
-DEFINE_BOOL(harmony_collections, false,
-            "enable harmony collections (sets, maps)")
 DEFINE_BOOL(harmony_generators, false, "enable harmony generators")
 DEFINE_BOOL(harmony_iteration, false, "enable harmony iteration (for-of)")
 DEFINE_BOOL(harmony_numeric_literals, false,
@@ -168,7 +166,6 @@ DEFINE_BOOL(harmony, false, "enable all harmony features")
 DEFINE_IMPLICATION(harmony, harmony_scoping)
 DEFINE_IMPLICATION(harmony, harmony_modules)
 DEFINE_IMPLICATION(harmony, harmony_proxies)
-DEFINE_IMPLICATION(harmony, harmony_collections)
 DEFINE_IMPLICATION(harmony, harmony_generators)
 DEFINE_IMPLICATION(harmony, harmony_numeric_literals)
 DEFINE_IMPLICATION(harmony, harmony_strings)
@@ -177,7 +174,6 @@ DEFINE_IMPLICATION(harmony, harmony_arrow_functions)
 DEFINE_IMPLICATION(harmony_modules, harmony_scoping)
 
 DEFINE_IMPLICATION(harmony, es_staging)
-DEFINE_IMPLICATION(es_staging, harmony_collections)
 DEFINE_IMPLICATION(es_staging, harmony_iteration)
 
 // Flags for experimental implementation features.