tighten SLB Xi_b line cuts
Currently the highest rate SLB HLT2 lines are the \Xi_b \to \Xi_c l \nu lines. We tighten the PID cuts on those lines and prescale their corresponding background lines further.
Testing the sprucing bandwidth shows only small gains, but that won't pick up on the fake line prescale (applied to the HLT2 line). I suspect this will have a much greater effect on the HLT2 line. I'll test that further in the morning.