The xorm `Sync2` has already been deprecated in favor of `Sync`,
so let's do the same inside the Gitea codebase.
Command used to replace everything:
```sh
for i in $(ag Sync2 --files-with-matches); do vim $i -c ':%sno/Sync2/Sync/g' -c ':wq'; done
```
Change all license headers to comply with REUSE specification.
Fix#16132
Co-authored-by: flynnnnnnnnnn <flynnnnnnnnnn@github>
Co-authored-by: John Olheiser <john.olheiser@gmail.com>
* delete attachments from the database and file system
* add migration
* fix import statements
* fix package name
* remove conditional should in case the confi has been changed and the server restarted
* simplify deletion of attachments in DB
* fix CI build
* fix review
* add copyright in the proper place
* fix review