remove moon calcs from database tutorial

[sbailey]

The spectroscopic-production-database.ipynb tutorial has some leftover code related to data quality vs. phase of the Moon. This was originally requested by me to have a tangible worked example, but at this point it is largely vestigial since it makes most sense in the context of per-exposure redshifts, which we never loaded into the DB anyway. I suggest that we remove that code, which will allow us to remove the desisurvey dependency and related things like setting $DESISURVEY_OUTPUT to a magic directory at NERSC, defining the "moon" function, etc. The rest of the tutorial which focuses on specific queries and mapping raw SQL into sqlalchemy operations is good, and removing the moon stuff will help focus the tutorial on the database itself rather than moon ephemeris details unrelated to the DB itself.