Revert to upstream amavis

This will have quite a knock-on effect as the quarantine location changes so does the conf location. Also we'd have to find somewhere else to package our version of the conf file e.g app-mail-filter-core or app-mail-antivirus-core both of which have a requires of amavisd-new.

At the same time the upstream package looks like it is reverting to the name amavis (when it goes to amavis-2.12.0-9).