Make newScheme non-final

Otherwise we always need to a clean compile to update things.

Author: odersky

compiler/src/dotty/tools/dotc/config/Config.scala

@@ -175,5 +175,5 @@ object Config {
   /** When in IDE, turn StaleSymbol errors into warnings instead of crashing */
   final val ignoreStaleInIDE = true
 
-  final val newScheme = true
+  val newScheme = false
 }