(bsc#1217173)
Remove environment variables DKIMPROXY_USER DKIMPROXY_GROUP.
These are hardcoded anyway in dkimproxy-tmpfiles. Changing these
would only lead to trouble. Now User and Group in dkimproxy-in.service
are set to dkim to avoid the mentioned security issue.
ExecStart got a '+' to execute it by root rights.
OBS-URL: https://build.opensuse.org/package/show/server:mail/dkimproxy?expand=0&rev=40
