sliding door hardware
The holes you're referring to are used for installation in some cases, but not all. It would depend on the door.
In most doors, once you unscrew the housing from the frame it should come out easily enough with a little encouragement. However there are some doors where it is necessary to remove the bottom rail first. In these cases you do have to be careful to avoid breaking the glass. After you remove the screw holding the bottom frame piece in place, you would take a mallet and block of wood and gently tap the rail off. You don't want to use too much force for obvious reasons, just enough to get the rail off.
Keep in mind that I don't know if this is the kind of door you have, I'm just explaining the two most common scenarios you'll encounter for patio glass door rollers.