It's not on every installation disc (some contain all JJ2 files, some just contain an installer), but if it's not you can just reinstall the game to get the file back. If you don't have an installation disc, there's countless ways to acquire a JJ2 installer... but it's not allowed to upload Anims.j2a to J2O, since you should be able to easily acquire it by yourself if you own the game.

It becomes kind of grey area for custom J2A's, but I think we have yet to see one appear on J2O.

Bottom line, always make backups