ia64: revert __node_random addition

This partially reverts commit 4ec37de8
("[IA64] Fix build breakage"), since the commit that made it necessary
got reverted earlier (see commit 35926ff5, 'Revert "cpusets:
randomize node rotor used in cpuset_mem_spread_node()"')

Even if we ever re-introduce this, there is no reason to make
__node_random be some architecture-specific function.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>