[SCSI] Unexport scsi/scsi.h from headers_install

The scsi/scsi.h header is normally provided by the libc (and was not
exported by the kernel since 2.6.24) and has been until it was
re-exported with 2.6.31.  The kernel version is not userspace clean and
does not appear to provide anything useable in userland over the
(e)glibc version.

Signed-off-by: Tom Rini <tom_rini@mentor.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>