www-servers/automx2: Change category to net-mail

www-servers/automx2: Change category to net-mail

Move existing Gentoo package www-servers/automx2 to net-mail/automx2.
Reasons for this change are as follows:

* Package automx2 replaces package net-mail/automx, which has already
  been last-rited.

* Some developers raised objections against using www-servers/automx2.
  While automx2 is a web service and hence uses web server technology,
  it is not a web server in the way www-servers is understood.

As per https://devmanual.gentoo.org/ebuild-maintenance/package-moves/index.html
all changes are deliberately combined into a single commit to ensure
atomicity during the update.

Signed-off-by: Ralph Seichter <gentoo@seichter.de>
Closes: https://github.com/gentoo/gentoo/pull/15011
Signed-off-by: Marc Schiffbauer <mschiff@gentoo.org>