Make read_antennas return positions from db, not csv file.

[david-deboer]

In file geo_sysdef.py, read_antennas returns all antenna positions as read from the csv file that specifies the positions, rather than the database. These are the same, but the position-of-record is in the database, so those values should be used. Two changes: (1) change the function to use the db, (2) make sure the positions are all in the database.