Instead of adding stat agentMS in all kinds of places, calculate it instead in the main Scene.Update() loop, like the other stats

Some of the places where agentMS was added were in separate threads launched by the update loop.  I don't believe this is correct, since such threads are no longer contributing to frame time.
Some of the places were also driven by client input rather than the scene loop.  I don't believe it's appropriate to add this kind of stuff to scene loop stats.
These changes hopefully have the nice affect of making the broken out frame stats actually add up to the total frame time

OpenSim/Region/Framework/Scenes/SimStatsReporter.cs

@@ -452,12 +452,6 @@ namespace OpenSim.Region.Framework.Scenes
             AddOutPackets(outPackets);
             AddunAckedBytes(unAckedBytes);
         }
-        
-        public void AddAgentTime(int ms)
-        {
-            addFrameMS(ms);
-            addAgentMS(ms);
-        }
 
         #endregion
     }