The NIP96 upload file is here:
https://github.com/haorendashu/nostr_sdk/blob/master/lib/upload/nip96_uploader.dart

I upload a test file and try to delete it.
1. Upload success.
2. Download success.
3. It seems first time i try to delete at https://nostr.build/delete/ it tell me *delete success* . 
4. But this file still can download.
5. And i try to delete this file again, it try me delete fail.

upload info:
file name: b89ad7e9d01d7002051847ac3762bb5b2191d9ae32b5df363d04545755892aa0.png
npub name: npub13jyr30u0x6uxzdcta0p2eh5dza0jhkglpp7mk3z7maej0ycamxgqw0y824