fix various things based upon changes in astropy

[lspitler]

Fixes a few things that have changed in astropy:

• wcs._naxis1 is no longer used. replaced with wcs.pixel_shape
• np.where doesn't strip astropy.units anymore
• astropy.units unit test issue related to approx
• small fix to array equal utility
• fixed fixture and duplicate test function definition, probably resulting from a past Merge of ImageSim into develop