aio: revert the workaround for bug 251828 in the tests

This bug is no longer reproducible in 14.0-CURRENT and 13.0-RELEASE

PR: 251828
Reported by: markj
Reviewed by: markj
Sponsored by: Axcient
Differential Revision: https://reviews.freebsd.org/D31535

(cherry picked from commit 825fb07c55986971b1a20e40a73c12eb0ff432e0)