pkg-stage.sh: Remove kde entirely

The package set for FreeBSD 13.5 comes from the 2025Q1 branch, which
doesn't have the new x11/kde (aka KDE 6) port; but shipping x11/kde5
(which is still in the 2025Q1 branch) doesn't make much sense either
since a few weeks after the release that will no longer be available
in either "latest" or "quarterly" package sets.

Just remove KDE packages from the 13.5 DVD entirely; this also makes
the DVD image fit into 4.7 GB size limit of physical DVDs again.

Direct commit to releng/13.5.

With hat: re
Approved by: re (cperciva)
Fixes: ee6c7bf50b93 ("pkg-stage.sh: kde5 -> kde")
Sponsored by: Amazon