MNT: Undo disable lazy loading hack in stpyfits, maybe

[pllim]

The hack was put in via 678c4ee when astropy.io.fits went to lazy loading (I think it was astropy/astropy#6082). I found an old note to investigate further, which I never got to. I vaguely remember looking at stpyfits and concluded that some significant refactoring might be necessary if we're going to do this the right way.

However, maybe removing the hack is not worth the time given that everything is working fine and the hack was a simple one-liner. But then again, if this hack breaks in the future or we find that it is no longer sufficient for "big data" or whatever, we might need to revisit, so hopefully this issue will be helpful then.

Notes to reproduce the problem without this hack

Example given by @stsci-hack on 2017-06-13, "The image I used to demonstrate the problem was nothing special, simply a RAW ACS image... This problem was easily reproduced using any RAW FITS file retrieved from the archive."

>>> from stsci.tools import stpyfits as sfits
>>> from drizzlepac import resetbits
>>> r = resetbits.reset_dq_bits('j9bc59wfq_raw.fits',4096, extver=1,extname='DQ')

.../hstdp-2017.2-2/lib/python3.5/site-packages/drizzlepac/resetbits.py
in reset_dq_bits(input, bits, extver, extname)
     150         for extn in extver:
     151             dqarr = p[extname,extn].data
--> 152             dqdtype = dqarr.dtype
     153             # reset the desired bits
     154             p[extname,extn].data = (dqarr &
~bits).astype(dqdtype) # preserve original dtype

AttributeError: 'NoneType' object has no attribute 'dtype'

>>> fimg = sfits.open('j9bc59wfq_raw.fits')
>>> fimg.info()

Filename: j9bc59wfq_raw.fits
No.    Name         Type      Cards   Dimensions   Format
   0  PRIMARY     PrimaryHDU     221   ()
   1  SCI         ImageHDU       146   (200, 200)   int16
   2  ERR         ImageHDU        58   ()
   3  DQ          ImageHDU        50   ()
   4  WCSCORR     BinTableHDU     59   7R x 24C   [40A, I, A, 24A, 24A,
24A, 24A, D, D, D, D, D, D, D, D, 24A, 24A, D, D, D, D, J, 40A, 128A]