sim: clean up CountedDrainEvent slightly.

There's no reason for it to derive from SimLoopExitEvent.
This whole drain thing needs to be redone eventually,
but this is a stopgap to make later changes to
SimLoopExitEvent feasible.

src/sim/sim_events.cc

@@ -85,14 +85,14 @@ exitSimLoop(const std::string &message, int exit_code, Tick when, Tick repeat)
 }
 
 CountedDrainEvent::CountedDrainEvent()
-    : SimLoopExitEvent("Finished drain", 0), count(0)
+    : count(0)
 { }
 
 void
 CountedDrainEvent::process()
 {
     if (--count == 0)
-        exitSimLoop(cause, code);
+        exitSimLoop("Finished drain", 0);
 }
 
 //

src/sim/sim_events.hh

@@ -55,7 +55,7 @@ class SimLoopExitEvent : public Event
     virtual const char *description() const;
 };
 
-class CountedDrainEvent : public SimLoopExitEvent
+class CountedDrainEvent : public Event
 {
   private:
     // Count of how many objects have not yet drained