I don't know but what you seem to be describing is a trim to make the brake drum look better as it can probably be seen through the wheel.

It should not be necessary to remove this in order to remove the drum - mostly what prevents the removal of a brake drum is a wear and corrosion ridge at the edge of the inside (braking area) and the brake shoes adjust behind the ridge.
Prior to the removal of the drum the brake shoe adjuster must be backed off or deactivated. Doing this usually means releasing the parking brake cable and then working through whatever hole is provided either in the backplate or drum.