TPG.Rounds.CleanupMap

Clear the map between rounds, leaving spectators' builds standing. game.CleanUpMap has no per-entity opt-out -- its only filter is by class, and a spectator's props are the same prop_physics as everyone else's -- so exempting an owner means not calling it. That is a real cost: it also restores map entities to their starting state, and a hand-rolled sweep does not. So it is still the path taken whenever no spectator owns anything, which is nearly every round; the sweep is the exception, not the rule. The sweep fires PreCleanupMap/PostCleanupMap itself, because addons (ACE and CFW among them) drop cached state on those and would otherwise be left holding references to entities that have gone.