Remove --supermixin flag from VM.

runtime/vm/parser.cc

Index: runtime/vm/parser.cc
diff --git a/runtime/vm/parser.cc b/runtime/vm/parser.cc
index 0da55d4bc84536559fc0b2ae82916413e94b8b27..a33c4cce1f4400cb53017017785efef1431204ac 100644
--- a/runtime/vm/parser.cc
+++ b/runtime/vm/parser.cc
@@ -44,7 +44,6 @@ DEFINE_FLAG(bool, enable_mirrors, true,
 DEFINE_FLAG(bool, load_deferred_eagerly, false,
     "Load deferred libraries eagerly.");
 DEFINE_FLAG(bool, trace_parser, false, "Trace parser operations.");
-DEFINE_FLAG(bool, supermixin, false, "Allow super calls in mixins.");
 DEFINE_FLAG(bool, warn_mixin_typedef, true, "Warning on legacy mixin typedef.");
 DEFINE_FLAG(bool, link_natives_lazily, false, "Link native calls lazily");
 
@@ -13843,16 +13842,6 @@ AstNode* Parser::ParsePrimary() {
       ReportError("class '%s' does not have a superclass",
                   String::Handle(Z, current_class().Name()).ToCString());
     }
-    if (!FLAG_supermixin) {
-      if (current_class().IsMixinApplication()) {
-        const Type& mixin_type = Type::Handle(Z, current_class().mixin());
-        if (mixin_type.type_class() == current_function().origin()) {
-          ReportError("method of mixin class '%s' may not refer to 'super'",
-                      String::Handle(Z, Class::Handle(Z,
-                          current_function().origin()).Name()).ToCString());
-        }
-      }
-    }
     const intptr_t super_pos = TokenPos();
     ConsumeToken();
     if (CurrentToken() == Token::kPERIOD) {