disable sys_timerfd() for 2.6.23

There is still some confusion and disagreement over what this interface should
actually do.  So it is best that we disable it in 2.6.23 until we get that
fully sorted out.

(sys_timerfd() was present in 2.6.22 but it was apparently broken, so here we
assume that nobody is using it yet).

Cc: Michael Kerrisk <mtk-manpages@gmx.net>
Cc: Davide Libenzi <davidel@xmailserver.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>