Remove all traces of pyfits from ics_ccdActor and ics_xcuActor

Modern astropy.io.fits is an unbelievable pig, and importing it brings in huge chunks of scipy and astropy among others. Besides that HDU writes are much slower. import and 4k*4k HDU append times for astropy.io.fits vs fitsio on a BEE are (30s, 1.5s) vs. (3s, 0.5s)

Right now I'm using fitsio for the hxActor and pyfits for the ccdActor. I'll unify on fitsio, even though the interface is sometimes more clumsy.