Use existing PVs for Aperture Scatterguard location

[DominicOram]

We are too strict on the current location of the aperture scatterguard, leaving us unable to move them. We can instead use the existing PVs to know where we are. The PVs are, each of these will go high if in the selected position:

• BL03I-MO-MAPT-01:Y:SMALL_CALC
• BL03I-MO-MAPT-01:Y:MEDIUM_CALC
• BL03I-MO-MAPT-01:Y:LARGE_CALC

Unfortunately there are is no equivalent for robot load, we can either do that manually based on the Y or add that in to controls too

Acceptance Criteria

• Reading the aperture scatterguard position is taken from the state of these PVs