Move blackBoxFile() testData to box/ directory

Delete all test methods (and empty test classes), since they'll be
auto-generated

compiler/testData/codegen/box/when/longInRange.kt

@@ -0,0 +1,9 @@
+class LongR {
+  fun contains(l : Long): Boolean = l == 5.toLong()
+}
+
+fun box(): String {
+  if (5 !in LongR()) return "fail 1"
+  if (6 in LongR()) return "fail 2"
+  return "OK"
+}