Remove the ExtDate library. It can't remain, because much of it is
based on Qt-3.x code, and therefore licensed under GPL v2 only. KDE
is migrating to GPL v3, which is not compatible with GPL v2.
KStars is already ported to use the new KDateTime classes. AFAIK, no
one else is using ExtDate (there is some usage in extragear, but those
programs use their own local fork of extdate).
TODO: After removing extdate, there are no more widgets defined in
libkdeedu/widgets. We could remove this directory, but I've left it
in for now in case we add widgets at some future date.