Revert following underlyingIfRepeated when matching

This was a left-over from a failed attempt to have OverridingPiars work exclusively by comparing signatures.
If we do that then repeated and underlying do have the same signature and therefore are supposed to match.
But as @retronym notes, this leads to problems. In any case, we no longer try to make overriding pairs
work that way, because it fails for other reasons as well.

Author: odersky

src/dotty/tools/dotc/core/TypeComparer.scala

@@ -680,7 +680,7 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling wi
     case formal1 :: rest1 =>
       formals2 match {
         case formal2 :: rest2 =>
-          (isSameType(formal1.underlyingIfRepeated(isJava1), formal2.underlyingIfRepeated(isJava2))
+          (isSameType(formal1, formal2)
             || isJava1 && (formal2 isRef ObjectClass) && (formal1 isRef AnyClass)
             || isJava2 && (formal1 isRef ObjectClass) && (formal2 isRef AnyClass)) &&
           matchingParams(rest1, rest2, isJava1, isJava2)