[HUGE DIFF] Remove unnecessary files from repo

[melissawm]

Remove .doctrees from all versions, and remove remaining files from older deployment workflow.

These files used to be deployed in the root of the repo, but now each version has its own folder so we should not keep them. We did not do this immediately due to concerns around redirection for the new napari.org/<version>/page URLs, but since it has been quite some time I think we can safely assume folks will land in the right pages.

[jni]

We discussed in docs-wg that we should only remove the doctrees for now, and we can discuss the old versionless deployment separately. @melissawm please ping when that's done and this is ready to merge! Or just merge. 😃

[melissawm]

@jni this is ready 👍🏻