Follow-up to 4bbae6e17
We're now using Zotero.HTTP.request(), which does its own checking for
security errors, so there's no need to do WebDAV-specific checks (though
we could consider checking for Zotero.HTTP.SecurityError and showing
more specific messages, since a self-signed certificate is more likely
in the case of WebDAV).
(cherry picked from commit f04a8c3736)
aa56ebae1a