SLB: Including bstoktaunu into bstokmunu and bstokenu lines

Line for Bs->KTauNu with tau->mu is one in the top of bandwidth usage. A line for Bs->KTauNu with tau->e is not existing and topo seems currently catching less than 3% of it. Therefore, discussed with @amathad to try the following:

• Lower muon pt cut and electron pt cut to 0.5 GeV, to include electrons and muons from tau decays into bstokmunu and bstokenu lines, respectively;
• removed the dedicated bstoktaunu HLT2 line.

Some bandwidth increase is expected for bstomunu and bstoenu. However, we will get rid of bstoktaunu. In addition, we are able to prescale SS independently for Bs->KTauNu decays (with current dedicated line SS and OS were together) and this should recover some bandwidth.