Ignore/disable Oracle class that is now mostly unused

library/lang/synthesis/Oracle.scala

@@ -8,6 +8,7 @@ import leon.lang._
 import scala.annotation._
 
 @implicitNotFound("No Oracle available for this source of non-determinism, please provide an implicit arg <: Oracle[T]")
+@ignore
 @library
 abstract class Oracle[T] {
   def head: T = this match {
@@ -26,5 +27,7 @@ abstract class Oracle[T] {
   }
 }
 
+@ignore
 case class Node[T](l: Oracle[T], v: T, r: Oracle[T]) extends Oracle[T];
+@ignore
 case class Leaf[T](v: T) extends Oracle[T];