Revert "Explicitly enable PRIu64 by defining __STDC_FORMAT_MACROS if it isn't"

This reverts commit d1b5d3b0e885ef057643fcea99bff8b6cce04b93.
Revert "Only include inttypes.h on platforms for which PRIu64 isn't in stdint.h"

This reverts commit e7778e08878d0c61903205428eeb131db9d11b3c.