These were broken since 2016:
f0367da7d1
since StartLimitIntervalSec got moved into [Unit] from [Service].
StartLimitBurst has also been moved accordingly, so let's fix that one
too.
NixOS systems have been producing logs such as:
/nix/store/wf98r55aszi1bkmln1lvdbp7znsfr70i-unit-caddy.service/caddy.service:31:
Unknown key name 'StartLimitIntervalSec' in section 'Service', ignoring.
I have also removed some unnecessary duplication in units disabling
rate limiting since setting either interval or burst to zero disables it
(ad16158c10/src/basic/ratelimit.c (L16))
