Remove fcntl wrapper

Replace the questionnable sync_file_range wrapper by more descriptive
util functions. Remove the unimplemented splice wrapper, I'd rather have
a build failure / adjust the build system on some platforms than have
hard to diagnose runtime issues.

Change-Id: I4114d0d9765ae3d95a1488c945e5d66a20c2029d
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>