systemd provides already provides all the fonctionnalities of spawn-fcgi
with the exception of the possibility to spawn multiple process to a
single socket (it can be done using multiwatch though). So we might as
well use the fonctions provided by systemd instead of needing to install
a new package and add a layer of indirection in how the fastcgi service
is managed.
This make for a somewhat simpler service that can be started as an
unprivileged user.
