Drop ineffective condition

The dropped condition is vacuously true for all singleton prefixes, since for them
classSymbol is NoSymbol. If we make it work as was intended using widen in front of
classSymbol on both sides, then EeraseAnd and dotty bootstrap fail.

Author: odersky

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

@@ -2378,7 +2378,7 @@ object Types {
     /** A reference like this one, but with the given prefix. */
     final def withPrefix(prefix: Type)(using Context): NamedType = {
       def reload(): NamedType = {
-        val allowPrivate = !lastSymbol.exists || lastSymbol.is(Private) && prefix.classSymbol == this.prefix.classSymbol
+        val allowPrivate = !lastSymbol.exists || lastSymbol.is(Private)
         var d = memberDenot(prefix, name, allowPrivate)
         if (d.isOverloaded && lastSymbol.exists)
           d = disambiguate(d,