test: remove flaky designation for test on AIX

https://github.com/nodejs/node/issues/5085 has been completed so
presumably test-fs-watch is not flaky on AIX anymore. Remove flaky
designation from sequential.status.

PR-URL: https://github.com/nodejs/node/pull/12564


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>