Fix 2 of the failed tests. Cause terrain queries to return null when no

terrain is found, rather than a default "0" terrain.
Remove the "remove object wrong region" test. UUIDs either are unique
or they're not. This test tested a bad behavior I have chosen not to 
duplicate.

OpenSim/Data/MySQL/MySQLRegionData.cs

@@ -507,7 +507,7 @@ namespace OpenSim.Data.MySQL
                 }
             }
 
-            return terrain;
+            return null;
         }
 
         public void RemoveLandObject(UUID globalID)