aio: remove INIT_KIOCTX

Unused after 20dcae32 aka
"[PATCH] aio: remove kioctx from mm_struct".

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>