Disable the use of VC*Companion super classes for now

They declare final methods which are overriden in SyntheticMethods,
which means that all value classes fail at runtime.
Disabling them makes it possible to add run tests for value classes
which will make it easier to experiment with changes to value classes.

Author: smarter

src/dotty/tools/dotc/transform/ExtensionMethods.scala

@@ -88,11 +88,11 @@ class ExtensionMethods extends MiniPhaseTransform with DenotTransformer with Ful
             decls1.enter(evt2uSym)
           }
 
-          // add a VCXXXCompanion superclass
-
+          // Add the extension methods, the cast methods u2evt$ and evt2u$, and a VC*Companion superclass
           moduleClassSym.copySymDenotation(info =
             cinfo.derivedClassInfo(
-              classParents = ctx.normalizeToClassRefs(List(newSuperClass), moduleSym, decls1),
+              // FIXME: use of VC*Companion superclasses is disabled until the conflicts with SyntheticMethods are solved.
+              //classParents = ctx.normalizeToClassRefs(List(newSuperClass), moduleSym, decls1),
               decls = decls1))
         case _ =>
           moduleClassSym