release: Ship DVD with only emacs@nox flavour

Contrary to the claim made in a previous commit, removing KDE and
adding all of vim and emacs results in an image which does not fit
into 4.7 GB; to be specific, it lands at 4.722 GB rather than the
claimed 4.689 GB.  (This descrepancy resulted from doing test DVD
image builds using an out-of-date tree, and became visible when the
15.0-RC3 images were built.)

Limit the emacs packages shipped on the DVD to the "nox" flavor;
this brings the disk image down to 4.407 GB, aka under the 4.7 GB
limit for standard DVDs.

Fixes:	6cc6beb4c8 ("release: Remove KDE from dvd1.iso")
MFC after:	1 day (for 15.0-RC4)

release/scripts/pkg-stage.sh

@@ -15,7 +15,7 @@ export PORTSDIR="${PORTSDIR:-/usr/ports}"
 
 _DVD_PACKAGES="
 devel/git@lite
-editors/emacs
+editors/emacs@nox
 editors/vim
 misc/freebsd-doc-all
 net/mpd5