Allow HDUs to not be loaded at close() to gain full benefit of lazy loading #5582
Description
#5065 implemented lazy loading of HDUs in fits files. But it did it in a way that maintains backwards compatibility at the expense of performance (See #5065 (comment) and other discussion in #4634). So we should consider removing that compatibility bit. It's been deprecated for 1.3 so it might make sense to slate this for 2.0...?