tidy `napari` classifiers

[alessandrofelder]

• remove from brainreg-segment and brainreg-napari
• add to brainreg

[willGraham01]

• [x] Remove from brainreg-segment
• [ ] Remove from brainreg-napari https://github.com/brainglobe/brainreg-napari/pull/79
• [x] https://github.com/brainglobe/brainreg/issues/167 (Add to brainreg)

[willGraham01]

brainreg-segment is going to be tricky to remove since we're recycled the repository name.

I think the best way to do this is for someone (me) to check out 04bc1a29c19a51e6d6679904644e07077b9bd68f locally, then create a new branch off here to update the OLD brainreg-segment package, and push this to PyPI manually.

This branch can then also be pushed to the remote (and marked as old/retired/stale) in the event that we need to perform further updates to the old-named package.

^ This doesn't work since I'm not a maintainer of brainreg-segment on PyPI (yet)

[willGraham01]

brainreg-napari will have to be un-archived, updated, then re-archived to achieve this.