Switch from /usr/home to /home as default home directory on FreeBSD

Summary:
Historically, FreeBSD has created home directories under /usr/home,
with a symlink from /home to /usr/home. That choice was motivated
when an UFS partition was divided into labels, with / relatively
small, and /usr larger. This is less relevant with one big partition.

This change acknowledges that change, and fixes an issue when creating
ZFS datasets for home directories: on new FreeBSD 14 installations,
to create <pool>/usr/home/<username> dataset would fail, as <pool>/usr/home
does not exist.

References:

• https://cgit.freebsd.org/src/commit/?id=bbb2d2ce4220
• https://www.freebsd.org/releases/14.0R/relnotes/

Test Plan: Tested on new WindRiver installation

Reviewers: aceppaluni, DorianWinty

Reviewed By: DorianWinty

Subscribers: DorianWinty

Maniphest Tasks: T2017

Differential Revision: https://devcentral.nasqueron.org/D3446