Revert "Fix #580: use isContainedIn to support cases where the enclosing class is also the top-level class"

This reverts commit 6898d2c.

Author: odersky

src/dotty/tools/dotc/transform/LambdaLift.scala

@@ -292,7 +292,7 @@ class LambdaLift extends MiniPhase with IdentityDenotTransformer { thisTransform
             val encClass = local.enclosingClass
             val topClass = local.topLevelClass
               // member of a static object
-            if (encClass.isStatic && encClass.isContainedIn(topClass)) {
+            if (encClass.isStatic && encClass.isProperlyContainedIn(topClass)) {
                // though the second condition seems weird, it's not true for symbols which are defined in some
                // weird combinations of super calls.
               (encClass, EmptyFlags)