nrelease: replace cvsup with pkgsrc/net/csup (Re: make nrelease: get rid of cvsup; we no longer depend on it)

[YONETANI Tomokazu <qhwt+dfly@xxxxxxxxxx>]

Hello.

This has completely slipped my mind, but here's an updated version:
  http://gitweb.dragonflybsd.org/~y0netan1/dragonfly.git/commit/911bb15d8c191e1b513881d0f6aa9be54911549c

It replaces cvsup with pkgsrc/net/csup, removes unused `fetch' target,
and stop populating /usr/local.  Although we have a git-snapshot of
pkgsrc tree, having CVSup client in the installer may benefit a user
who don't want the extra 80M or so bytes for its git repository.
And it runs on x86_64, too.  For people who do want to download CVS
repositories, well, they can use devel/cvsync, which is available in
the pkgsrc collection.

Oh by the way, we still have the following entry in UPDATING file:

> Upgrading to DragonFly from FreeBSD

Do we still support this upgrading path in the first place?  If not,
I'll simply drop this entry.  If we do, we need to update it.  Currently
it explains how to download the CVS repository of DragonFly source tree
and checkout from it locally, but as far as I know we've never published
a CVS-mirror of our git repository, so mayb s/he finds a mirror of very
old CVS repository and surprise.