Cleanup and cut changes to BdsToVV and BdsTohhhh lines

Some tidying up of comments (and commented-out cuts) removed from BdsToVV.py and BdsTohhhh.py.

Re-implemented the mipchi2_max cut for BdsToVV lines and put an optional mipchi2_max argument in make_twobody in builders/combiners.py which reduces the B->VV line rate by about half.

Re-implemented some cuts in make_rho0 in builders/basic_builder.py.

Put some basic values for the new vtx_am_min(max) arguments (50 MeV tighter than am_min(max)).

assigned to @pbaladro

mentioned in merge request !1333 (merged)

approved this merge request

merged

mentioned in commit f97ad82a