ipc namespace: remove config ipc ns fix

Finish the work : kill all #ifdef CONFIG_IPC_NS.

Thanks Robert !

Signed-off-by: Cedric Le Goater <clg@fr.ibm.com>
Cc: Eric Biederman <ebiederm@xmision.com>
Cc: Robert P. J. Day <rpjday@mindspring.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>