mail-filter/milter-regex: Bump to version 2.7

mail-filter/milter-regex: Bump to version 2.7

The new version implements a "-t" command line option, allowing
configuration files being tested for correctness before launch.
This new feature is now used in the init.d file.

The ebuild no longer relies on user.eclass but uses a acct-user
dependency, as per GLEP81.

Package-Manager: Portage-2.3.79, Repoman-2.3.16
Signed-off-by: Ralph Seichter <gentoo@seichter.de>
Closes: https://github.com/gentoo/gentoo/pull/13964
Signed-off-by: Joonas Niilola <juippis@gentoo.org>