Nix XRam cruft. Does nothing on iOS.
Nix some stray debug logging.
Read uncompressed audio via mmap() if possible.

Even if we can't mmap() it, this code still results in fewer copies and
instructs iOS to avoid caching the file data. This yields faster, more
predictable load times, no speedup on subsequent reads, which is usually the
right desired for games, which manage their own caches.