First open a blank (new) document, then select the door tool. Open the door tool preferences, and select bi-parting door, and Parts. Now set the astragal sizes to 0 (zero). While you're at it set all the other parts to the sizes you prefer. Do the same exercise for the other door types, until you have the defaults set just as you prefer them to be. Now save the (still blank) drawing as a Template, and when you use it in future there will be no astragals in the bi-parting doors.
If you already have templates made - say for different page sizes, or with title blocks - simply open the existing template, make your adjustments to the door preferences, and Save as Template use the same name (replacing the original). It's worth doing a similar exercise for windows also, particularly if you work in metric units, because most of the VW "standard" part sizes are based on imperial.