Revert "Replace isLambdaSub with hasSimpleKind"

This reverts commit 283f261 because it
introduces failures (which I don't get yet), as also shown in
http://dotty-ci.epfl.ch/lampepfl/dotty/5085/4.

Author: Blaisorblade

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

@@ -380,7 +380,7 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
           if (cls2.typeParams.isEmpty) {
             if (cls2 eq AnyKindClass) return true
             if (tp1.isRef(NothingClass)) return true
-            if (!tp1.hasSimpleKind) return false
+            if (tp1.isLambdaSub) return false
             if (cls2 eq AnyClass) return true
               // Note: We would like to replace this by `if (tp1.hasHigherKind)`
               // but right now we cannot since some parts of the standard library rely on the