MIPS: SGI-IP27: remove not used stuff inherited from IRIX

Most of the SN/SN0 header files are inherited from IRIX header files,
but not all of that stuff is useful for Linux. Remove not used parts.

Signed-off-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: James Hogan <jhogan@kernel.org>
Cc: linux-mips@vger.kernel.org
Cc: linux-kernel@vger.kernel.org