Remove unimplementated UpdateMovement() methods from SOG, SOP.

SP still has an implementation but this is now just a public method on SP rather than an abstract one in EntityBase.
No point making the code more complex until it actually needs to be,

OpenSim/Region/Framework/Scenes/SceneObjectPart.cs

@@ -4189,10 +4189,6 @@ namespace OpenSim.Region.Framework.Scenes
             }
         }
 
-        public virtual void UpdateMovement()
-        {
-        }
-
         /// <summary>
         ///
         /// </summary>