configure: remove aio.h check

configure: remove aio.h check

Remove the configure check for aio.h, which is not provided by uClibc, and
which does not appear to be used by xfsprogs.

Refer to Gentoo Bug #477758:
https://bugs.gentoo.org/show_bug.cgi?id=477758

Signed-off-by: Joshua Kinard <kumba@gentoo.org>
Reported-by: El Goretto <el.goretto@free.fr>
Suggested-by: René Rhéaume <rene.rheaume@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <david@fromorbit.com>