debt: remove unused dead code (tldraw#8763)

i had claude use knip as a low pass filter, and do some AST wrangling to
find some dead code in the project, inspired by finding out the
`GeometryDebuggingView` was dead code around the old non `overlayUtils`
debug drawing paths. found some other unused relics.

### Change type

- [ ] `bugfix`
- [ ] `improvement`
- [ ] `feature`
- [ ] `api`
- [x] `other`

Author: kostyafarber