Right now, users with the capability mod/wiki:managefiles can delete files from a wiki without even creating a log entry in the Moodle logs.

There is also no capability to control a role's ability to delete files without taking away their ability to add files.

Since adding files is very useful for students, I therefore suggest splitting the capability mod/wiki:managefiles into mod/wiki:addfiles and mod/wiki:deletefiles.

Testing instructions:

1. Grant students the capability mod/wiki:addfiles
2. Add files to a wiki as a student
3. Try deleting files again - deleting files should not work