They aren’t needed once the child has head control. If there are other issues (such as Trace’s torticollis) then it’s still ok to have them in there.
If at any point in time it’s interfering with the harness straps, and you being able to adjust them to the tightness they need to be then it MUST go at that point. If you MUST take it out and you still need the head support of it, then use a rolled receiving blanket and shape it into an upside down “U” around the child’s head so that it doesn’t interfere with the harness.