Core/Units: moved cyclic spline synchronization mechanic heartbeat handling

Port From (https://github.com/TrinityCore/TrinityCore/commit/c2fedbb6cc89510002e9f56751e7f8427e306487)

Source/Game/Entities/Unit/Unit.cs

@@ -70,8 +70,6 @@ namespace Game.Entities
 
             m_serverSideVisibility.SetValue(ServerSideVisibilityType.Ghost, GhostVisibilityType.Alive);
 
-            splineSyncTimer = new TimeTracker();
-
             m_unitData = new UnitData();
         }
 
@@ -2557,6 +2555,14 @@ namespace Game.Entities
             return m_deathState;
         }
 
+        public override void Heartbeat()
+        {
+            base.Heartbeat();
+
+            // SMSG_FLIGHT_SPLINE_SYNC for cyclic splines
+            SendFlightSplineSyncUpdate();
+        }
+
         public bool HaveOffhandWeapon()
         {
             if (IsTypeId(TypeId.Player))