Tighten Bc2BsPi/K lines
The SLB Bc->BsPi/K lines are among the top lines taking rate in the full stream, and show only weak Ds mass peaks in the monitoring of mu=5.3 data. This MR applies some generally reasonable cuts (known to be such from the Bs2DsK analysis) to tighten them. Impact to be tested.
Note that while the B pointing angle cut might be debatable since the Bc flies, the Bc lifetime is still so short that this should be fine.
Impact to be tested.