Update combine_da_to_da in MONET

[rschwant]

The develop_aircraft branch still uses a new branch (dev-combine_to_da) on MONET which has combine_da_to_da that Barry wrote for us. Once this is well tested we need to move this to the main branch of MONET, so that it can be run through conda like the rest of MELODIES MONET

This can be done later once we are ready to push develop_aircraft to develop for the first time.

https://github.com/noaa-oar-arl/monet/blob/dev-combine_to_da/monet/util/combinetool.py

[rschwant]

This capability is now in MONET develop branch, so this can be closed.
noaa-oar-arl/monet#121