Simplify VM internal representation of a mixin application clause (MixinAppType

tests/language/mixin_type_parameters_errors_test.dart

Index: tests/language/mixin_type_parameters_errors_test.dart
===================================================================
--- tests/language/mixin_type_parameters_errors_test.dart	(revision 27361)
+++ tests/language/mixin_type_parameters_errors_test.dart	(working copy)
@@ -6,11 +6,11 @@
 class M<U> { }
 
 class A<X> extends S<int> with M<double> { }
-class B<U, V> extends S with M<U, V> { }  /// 01: compile-time error
-class C<A, B> extends S<A, int> with M { }  /// 02: compile-time error
+class B<U, V> extends S with M<U, V> { }  /// 01: static type warning
+class C<A, B> extends S<A, int> with M { }  /// 02: static type warning
 
 typedef F<X> = S<X> with M<X>;
-typedef G = S<int> with M<double, double>;  /// 05: compile-time error
+typedef G = S<int> with M<double, double>;  /// 05: static type warning
 
 main() {
   var a;