do not export /usr/include/scsi in make headers_install

/usr/include/scsi is provided by glibc.
Remove the scsi export from make headers_install target.

Signed-off-by: Olaf Hering <olh@suse.de>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: James Bottomley <James.Bottomley@steeleye.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>