Move blackBoxFile() testData to box/ directory

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

compiler/testData/codegen/box/objects/kt3238.kt

@@ -0,0 +1,12 @@
+object Obj {
+    class Inner() {
+        fun ok() = "OK"
+    }
+}
+
+fun box() : String {
+    val klass = Class.forName("Obj\$Inner")!!
+    val cons = klass.getConstructors()!![0]
+    val inner = cons.newInstance(* Array(0){""})
+    return "OK"
+}