Revert "Committing the same fix here for the infinity problem on TPs."

This reverts commit f5343e4b07.

This is because a returning viewer by teleport before 15 seconds are up will be disrupted by the close and so is a significant behaviour change
Development along the longer delay lines will continue in dev code

OpenSim/Region/CoreModules/Framework/EntityTransfer/EntityTransferModule.cs

@@ -664,7 +664,7 @@ namespace OpenSim.Region.CoreModules.Framework.EntityTransfer
                 //
                 // This sleep can be increased if necessary.  However, whilst it's active,
                 // an agent cannot teleport back to this region if it has teleported away.
-                Thread.Sleep(15000);
+                Thread.Sleep(2000);
 
                 sp.Scene.IncomingCloseAgent(sp.UUID, false);
             }