Eliminate useless adjustments of aliased device.

No need to set any fields in the cloned device. devfs uses symlinks,
so the adev entries returned won't be presented to the drivers. Since
we don't save copies, nothing else will see them. This code came from
the old compat code, and it appears to be obsolete or never needed.

Submitted by: kib@
Differential Review: https://reviews.freebsd.org/D11919