Strenuous is a 57.5 kb file located in the FCP package. (Final Cut Pro > Content > Frameworks > Flexo.frameworks > Versions > A > Resources > Fonts) but it's also there in Motion and iMovie. You'll find the other offensive fonts there, too.
You can remove them but be advised you're monkeying with the FCP application bundle itself and it may fail to launch at all at a later date because it cannot locate something that should natively be there.
Another thing.... If you're tasked to work on a project someone supplies you where they HAVE used one of the fonts you removed you'll be screwed using a font FCP substitutes for the missing ones. Seems to be you're inviting a whole lot of headache there hunting down and removing a few fonts from the application itself to really any overall benefit. Cull system fonts but never application embedded ones.
Interesting ... I see nothing in the Fonts folder following the path that you've suggested, VTCMedia, both for FCPX and Motion - I do not have iMovie on this Mac. I am running Mojave (10.14.6) and FCPX (10.4.10). Perhaps my older system is why?
If I was able to see the font files, rather than delete, I would move the files to another folder so that I could return them if I ran into any problems in the future.
But thank you both for your feedback. Good points to consider. I guess I will leave things as is.