main/supervisor: fix dependencies

This is a fix for #12713 (closed).

According to several issues on the Supervisor project, setuptools is a runtime dependency and will continue to be so for the foreseeable future. This merge request removes py3-setuptools from the makedepends var and adds it to the depends var.

Also, meld3 is no longer used by Supervisor (archived on github), so I've removed py3-meld3 from the depends var.