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/kt2384.kt

@@ -0,0 +1,15 @@
+class A {
+    class object {
+        val b = 0
+        val c = b
+        
+        {
+            val d = b
+        }
+    }
+}
+
+fun box(): String {
+    A()
+    return if (A.c == A.b) "OK" else "Fail"
+}