Hello Guix!

As of 2017, IANA (www.iana.org) has changed the standard template for
font media types.

SOURCE: https://www.iana.org/assignments/media-types/media-types.xhtml#font

So, font/freetype and font/opentype has to be updated to font/ttf and
font/otf, respectively.

Almost all font packages in guix, are using the old specification. I
have updated font-gnu-freefont a while ago. We need to update other
packages. Any ideas on how to change them all in a time-saving way?

Thank you!

Regards,
RG.