Revert "WIP: GenericIO byte-swapping hacks"

This reverts commit ebdc0ed95f53a7072a5b7c021f5e512eed55d43f.
Revert "BUGFIX: swap headersize"

This reverts commit 8f3186a028c4a705d0148c7f2aa610d6103eec07.
Revert "ENH: Add swap endian facility in GenericIO"

This reverts commit 8365d17840f8ecf89ef101be295e1d96ac1f74bb.