The file must be a leftover from the beginning when OSMC had untracked by apt files and maybe some upgrade somehow cleaned the untracked file for some people. Which apt wouldn’t usually do so it is strange.
Even in all my cleaning of my system I wouldn’t of manually cleaned that file. I use Linux exclusively on my computers so I know a decent amount about it and have used that knowledge to keep my OSMC clean and running without re-installing at the first signs of trouble like some would.
I’m currently running this https://www.reddit.com/r/linux/comments/cki14/are_all_files_in_usr_are_tracked_by_your_package/ to check for any other important looking untracked files might be leftover in OSMC so they can be properly managed by apt in the future. If I find anything I’ll start a new thread since it may not be something to do with these test builds.