ia64: cleanup remove_siblinginfo()

remove_siblinginfo() initialises variable 'last', but never uses it.
Drop unneeded code.

CC: Ingo Molnar <mingo@kernel.org>
CC: Peter Zijlstra <peterz@infradead.org>
CC: Valentin Schneider <vschneid@redhat.com>
CC: linux-ia64@vger.kernel.org
CC: linux-kernel@vger.kernel.org
Signed-off-by: Yury Norov <yury.norov@gmail.com>
Acked-by: Andrew Morton <akpm@linux-foundation.org>