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/simpleObject.kt

@@ -0,0 +1,7 @@
+object A {
+  val x: Int = 610
+}
+
+fun box() : String {
+  return if (A.x != 610) "fail" else "OK"
+}