Generate hazzers for Ruby oneof fields in proto3

ruby/ext/google/protobuf_c/message.c

@@ -243,15 +243,6 @@ static int extract_method_call(VALUE method_name, Message* self,
   if (Match(m, name, f, o, "clear_", "")) return METHOD_CLEAR;
   if (Match(m, name, f, o, "has_", "?") &&
       (*o || (*f && upb_FieldDef_HasPresence(*f)))) {
-    // Disallow oneof hazzers for proto3.
-    // TODO(haberman): remove this test when we are enabling oneof hazzers for
-    // proto3.
-    if (*f && !upb_FieldDef_IsSubMessage(*f) &&
-        upb_FieldDef_RealContainingOneof(*f) &&
-        upb_MessageDef_Syntax(upb_FieldDef_ContainingType(*f)) !=
-            kUpb_Syntax_Proto2) {
-      return METHOD_UNKNOWN;
-    }
     return METHOD_PRESENCE;
   }
   if (Match(m, name, f, o, "", "_as_value") && *f &&