mailto: URLs in <contact> should not be deprecated with the given reasoning

[marcusmueller]

In the past, mailto: URL schemas to link to email addresses were also supported for this URL type. It is recommended to not use them in new metadata, as they provide poor usability on most systems when users click on such a link and no local email client is configured.

Not offering the user a good experience when clicking on the appropriate information on how to contact an author or project is not a shortcoming of the metadata, but of the GUI frontend.

There's enough projects out there with no website or a single author; enforcing metadata linking to something that is not actually the way to contact the author just because it's hard to do right in the GUI isn't the right choice here!