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)

OpenSim/Data/Tests/BasicRegionTest.cs

@@ -675,14 +675,6 @@ namespace OpenSim.Data.Tests
             Assert.That(t4, Is.Null);
         }
 
-        [Test]
-        public void T051_RemoveObjectWrongRegion()
-        {
-            db.RemoveObject(prim1, UUID.Random());
-            SceneObjectGroup sog = FindSOG("object1", region1);
-            Assert.That(sog, Is.Not.Null);
-        }
-
         [Test]
         public void T052_RemoveObject()
         {