Do not rewrite trait method calls to static helpers in Scala.js.

In Scala.js, even Scala 2 already relies on default methods, and
does not use static method helpers.

compiler/src/dotty/tools/dotc/transform/LinkScala2Impls.scala

@@ -75,7 +75,7 @@ class LinkScala2Impls extends MiniPhase with IdentityDenotTransformer { thisPhas
     def currentClass = ctx.owner.enclosingClass.asClass
     app match {
       case Apply(sel @ Select(Super(_, _), _), args)
-      if sel.symbol.owner.is(Scala2x) && currentClass.mixins.contains(sel.symbol.owner) =>
+      if sel.symbol.owner.is(Scala2x) && currentClass.mixins.contains(sel.symbol.owner) && !ctx.settings.scalajs.value =>
         val impl = implMethod(sel.symbol)
         if (impl.exists) Apply(ref(impl), This(currentClass) :: args).withSpan(app.span)
         else app // could have been an abstract method in a trait linked to from a super constructor