Incorrect license header in VGTbackbone.py

The header in [`DocumentUnderstanding/VGT/object_detection/ditod/VGTbackbone.py`](https://github.com/AlibabaResearch/AdvancedLiterateMachinery/blob/main/DocumentUnderstanding/VGT/object_detection/ditod/VGTbackbone.py) states that the code is under GPL/Commercial dual licensing from ETRI. The actual implementation is very different from the [original code](https://github.com/youngwanLEE/MPViT/blob/main/detectron2/mpvit/backbone.py) so I am not sure if it was left there accidentally or on purpose. Since this repository is under Apache 2.0, either that code can not be used or this header should be removed or the repository must be under a GPL license.