librados: don't use lockdep for AioCompletionImpl

This is a quick workaround for the next branch. A more complete fix
will be done for the master branch. This does not affect correctness,
just what qa runs with lockdep enabled do.

Signed-off-by: Josh Durgin <josh.durgin@inktank.com>
Reviewed-by: Sage Weil <sage.weil@inktank.com>