Move blackBoxFile() testData to box/ directory

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

compiler/testData/codegen/box/classes/kt249.kt

@@ -0,0 +1,13 @@
+package x
+
+class Outer() {
+    class object {
+        class Inner() {
+        }
+    }
+}
+
+fun box (): String {
+    val inner = Outer.Inner()
+    return "OK"
+}