Thank you for your post.
Short answer... the individual files in the bundle cannot be removed. It would be similar to going into the FileMaker application bundle and removing parts of codes. Since there were so many more features added since 8.5, the size of the application has increased.
What these are filesets for?
I'd still like to know the answer to my main question. (Hopefully, someone knows.)
The request has been sent to Development. I will post a reply when I hear something.