p9fs: remove duplicated code

This code is using the vnode after it has been released and causing a
panic when a p9fs shared volume is unmounted. In fact, it seems like it's
just duplicated code left behind from a bad merge.

PR: 279887
Reported by: Michael Dexter

Reviewed by: imp
Pull Request: https://github.com/freebsd/freebsd-src/pull/1323