Make activate_fd() and free_irq_by_irq_and_dev() static.  Remove
init_aio_irq() since it has no users.

Cc: Jeff Dike <jdike@addtoit.com>
Signed-off-by: NWANG Cong <wangcong@zeuux.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>