Better fix for FG#50
- The previous solution was not allowing the suspended actor to be resumed properly
- Instead of going for a complex story where we create an activity on
which to suspend the actor, simply unschedule it on suspend(), and
explicitely reschedule it on resume()
- This is much easier since we don't have to save and restore the
simcall of the suspended actor, even if the price to pay is the
explicit simix_global->actors_to_run.push_back(this); in resume()
of which I'm not a big fan.
Fixes https://framagit.org/simgrid/simgrid/-/issues/50
