pkg-stage.sh: kde5 -> kde

The "kde5" package no longer exists; KDE goes to 6.

Note: Depending on the size of 13.5-BETA3 DVD images, KDE might end
up being removed from this list in the near future.

Approved by: re (cperciva)
With hat: re@
MFC after: 30 seconds
Sponsored by: Amazon

(cherry picked from commit 0d7b98c06c5ec9638020844ee460af075cfc6e54)
(cherry picked from commit 1c2e947d272ea42dbf7416d867101fe5164ffc6d)