Retire mta_start_script

Hello everyone,

I do plan on retiring mta_start_script and what goes with it:
- /etc/rc.d/othermta

the othermta mecanism (calling mta_start_script if defined to something
different than /etc/rc.sendmail)

As far as I am aware all mta in the ports tree are not using this mecanism.

I do plan on just retiring all of this for FreeBSD 14.0.

If no argumented objections is made, I will retire next week.

Best regards,
Bapt