suricata: expose SuricataMainLoop and GlobalsDestroy

suricata: expose SuricataMainLoop and GlobalsDestroy

Expose SuricataMainLoop and GlobalsDestroy so that SuricataMain can be
replicated by a library user of Suricata.

These removes the `suricata` instance as a function argument to some
of these functions, as the way we use it now, it serves no
purpose. However, it is a reminder that it should probably be
refactored to not be a global, as at some point it might be desirable
for to have multiple instances active without data sharing.