Remove all extra files that are now unnecessary to the website. The files at the root of the repo (such as usage.html and others like tutorials/*) were acting as redirects to stable, and with a 404 page I think we can remove them. The .doctrees and _sources/ folders are not necessary to the website, so we can remove them here and also make sure they are not copied over from commits to napari/napari and napari/docs (in a follow up PR)
Closes https://github.com/napari/napari-sphinx-theme/issues/125
This is a proposal to