Update DiLepFlags.py to add HLT_2g50_loose
The trigger HLT_2g50_loose changed L1 in 2017, and the old one was lost from our filters -- this MR adds the original HLT_2g50_loose back into the filter to cover the 2015+2016 data.
The trigger HLT_2g50_loose changed L1 in 2017, and the old one was lost from our filters -- this MR adds the original HLT_2g50_loose back into the filter to cover the 2015+2016 data.