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/kt2719.kt

@@ -0,0 +1,9 @@
+class Clazz {
+    class object {
+        val a = object {
+            fun run(x: String) = x
+        }
+    }
+}
+
+fun box() = "OK"