aio: revert the workaround for bug 251828 in the tests

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

Do not MFC to stable/12 !

PR: 251828
Reported by: markj
Reviewed by: markj
MFC after: 2 weeks
Sponsored by: Axcient
Differential Revision: https://reviews.freebsd.org/D31535