Unfortunately the US library does not have this built into the double doors (as you have presumably discovered). There might be a way to tweak the single doors so the line doesn't show in plan but they will not schedule correctly (if that is an issue) and probably won't look quite right in elevation. I vaguely recall that the D3 "SmartParts Real Doors" library does have this feature but I can't say for sure.
You could model your own custom door and edit the symbol to suit your needs. The GDL manual has some instructions for this, and you could probably find more with a search here. This is not hard for a one off (in both specs and size) but could get tedious if you have many variations.
