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/SceneObjectGroup.cs

@@ -1005,13 +1005,6 @@ namespace OpenSim.Region.Framework.Scenes
             part.ClearUndoState();
         }
 
-        public override void UpdateMovement()
-        {
-            SceneObjectPart[] parts = m_parts.GetArray();
-            for (int i = 0; i < parts.Length; i++)
-                parts[i].UpdateMovement();
-        }
-
         public ushort GetTimeDilation()
         {
             return Utils.FloatToUInt16(m_scene.TimeDilation, 0.0f, 1.0f);