Revert "Make macros out of most byteswaps"

This reverts commit c6dd741f46037c206c4c4f57d1a75f7d219a726a.
Revert "Optimize for r_pixbytes == 1"

This reverts commit 8c001e390b41f4c89097aea68412ae0966ce2eb8.
Revert "Comment out prealspandrawer function pointer"

This reverts commit 212856b3b9d1f0771658c8437dc23d8de9e0d700.