I can think of two solutions atm taking into consideration an `olympus->ascraeus` migration:

1. Keep the constants, the language variables and the extension groups, and tell the users to manually change the `SPECIAL CATEGORY -> None` so that the download counter gets updated for these 3 outdated categories. It would be an overkill to make a check for these 3 categories in [file.php](https://github.com/phpbb/phpbb/blob/develop-ascraeus/phpBB/download/file.php#L296) just for a counter update.
But keeping the constants etc, will probably make the future decision of removing them more difficult.

2. Comment out the constants, loose the language variables and the extension groups and tell the users to manually move the file extensions to extension group: `Downloadable Files`

```
// outdated media constants - to be removed in 3.2
// define ...
```