Newer versions of Astropy Regions do not support read_ds9

[domase]

To make the streamline modeling code compatible with new versions of Astropy Regions, config.py needs to be updated in two places to remove references to read_ds9:

#from regions import read_ds9
from regions import Regions

#regions = read_ds9(region_file)
regions = Regions.read(region_file, format='ds9')