mail/fetchmail: fix rcscript regression from _1 that broke global mode

In a situation where fetchmail is to be started globally with the
configuration in $LOCALBASE/etc, the rc.d file would try to run
fetchmail for the wrong user.

Simplify script more, avoiding recursive call in single-user mode.

Submitted by: Corey Halpin (maintainer, direct mail to mandree@)
Reported by: Armin Tüting