Stop rewriting withFilter to filter

This was dropped for Scala 2 in scala/scala#5252 for
2.12.0-RC1, as discussed for instance in
scala/bug#6455 and
scala/bug#8339.

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -462,11 +462,6 @@ class Typer extends Namer
       // SI-3120 Java uses the same syntax, A.B, to express selection from the
       // value A and from the type A. We have to try both.
       selectWithFallback(tryJavaSelectOnType(_)) // !!! possibly exponential bcs of qualifier retyping
-    else if (tree.name == nme.withFilter && tree.getAttachment(desugar.MaybeFilter).isDefined)
-      selectWithFallback {
-        implicit ctx =>
-          typedSelect(untpd.cpy.Select(tree)(tree.qualifier, nme.filter), pt) // !!! possibly exponential bcs of qualifier retyping
-      }
     else
       typeSelectOnTerm(ctx)
   }

tests/untried/neg/t6455.scala → tests/neg/t6455.scala

@@ -2,5 +2,5 @@ object O { def filter(p: Int => Boolean): O.type = this }
 
 class Test {
   // should not compile because we no longer rewrite withFilter => filter under -Xfuture
-  O.withFilter(f => true)
+  O.withFilter(f => true) // error // error
 }