desi_purge_night should also delete future cumulative redshift directories

[akremin]

Currently, desi_purge_night is fairly straightforward and just removes night-level directories in several places. This doesn't, however, remove cumulative redshift directories from future nights that included the data being purged.

This is dangerous because the user may not realize that the purge didn't remove spectra, coadds, and redshifts that still use the data that was meant to be purged.

desi_purge_tilenight does this at the per-tile level. Consider either including some of that logic or iteratively calling that function for science tiles first.