[wildcard-variables][test] Fix wildcard language tests.

This CL fixes some bugs in a few tests and removes unnamed optional default tests.

Bug: #55652
Change-Id: I41be6eb2f45598803eaeddd99375aa9cdb3fa990
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/373324
Commit-Queue: Kallen Tu <kallentu@google.com>
Reviewed-by: Lasse Nielsen <lrn@google.com>

tests/language/wildcard_variables/initializing_formal_parameters/super_test.dart

@@ -13,7 +13,7 @@ void main() {
   var c = C(1);
   Expect.equals(1, c._);
 
-  var cWithPositional = C.withPositional(1, 100);
+  var cWithPositional = C.superAndPositional(1, 100);
   Expect.equals(1, cWithPositional._);
 
   var multipleSuperParameters = MultipleSuperParameters(1, 2, 3);

tests/language/wildcard_variables/non_binding/class_members_test.dart

@@ -45,10 +45,7 @@ class StaticMember {
     var (_, _) = (3, '4');
     Expect.equals(2, _);
 
-    _ = 4;
-    Expect.equals(4, _);
-
     int foo<_>([int _ = _ + 1]) => _;
-    Expect.equals(4, foo());
+    Expect.equals(2, foo());
   }
 }