webdav: review sample URLs

[jorgeorpinel]

Extracted from #1695 (review)

WebDAV seems to be setup as any HTTP server so no need for public.php samples in our docs (as they exist now from #1617).

UPDATE: From #1695 (comment):

public.php is a public endpoint for Nextcloud and Owncloud... good to keep one as an example, as most of our WebDAV users are either using Owncloud or Nextcloud.

[jorgeorpinel]

From https://doc.owncloud.org/server/9.0/user_manual/files/access_webdav.html:

example.com/owncloud/remote.php/dav/files/USERNAME/
https://example.com/owncloud/public.php/dav

From https://docs.nextcloud.com/server/15/user_manual/files/access_webdav.html:

example.com/nextcloud/remote.php/dav/files/USERNAME/
https://example.com/nextcloud/public.php/webdav