Update line pump rates and esc. prob at all times

To improve performance, Cloudy updates spectral line pump rates and escape probabilities only once per zone, controlled with the flags conv.lgFirstSweepThisZone and .lgLastSweepThisZone.

This design choice is old, and the performance gains may now longer be as important as they once were. In addition, it is known to prevent masers from converging.

Remove the flags from the update logic to always carry it out when a zone is processed, and from Cloudy's namespace altogether, since they are not used otherwise.