This has cropped before and it seems as though many don't have the loop. But the L42's here, on the sniper div had them and so did all those that I ever encountered. I say this because the L42 EMER didn't mention that it could be removed - so it stayed.
I never used the trigger guard screw swivel (and I was never a sniper) but the reason it was retained was so that the sling didn't twist.