Fixed debugging checks broken after the last changes to the recv_spart task.

src/runner.c

@@ -2945,12 +2945,6 @@ void runner_do_recv_spart(struct runner *r, struct cell *c, int clear_sorts,
   }
 
 #ifdef SWIFT_DEBUG_CHECKS
-  if (ti_gravity_end_min < ti_current)
-    error(
-        "Received a cell at an incorrect time c->ti_end_min=%lld, "
-        "e->ti_current=%lld.",
-        ti_gravity_end_min, ti_current);
-
   if (ti_stars_end_min < ti_current)
     error(
         "Received a cell at an incorrect time c->ti_end_min=%lld, "