[IA64-SGI] remove unused sn header files

This patch makes Jes' patch (which also contains the removal of fetchop.h) a
bit smaller, and removes two other unused files at the same time, sndrv.h and
sn_fru.h.

Signed-off-by: Jesse Barnes <jbarnes@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>