sh: Remove /.profile

root's home directory was moved to /root many years ago, so there's no
reason to keep this old link. This brings sh in line with csh, where
/.cshrc was removed in dcb65c5a94d4.

Relnotes: yes
Approved by: re (cperciva)
MFC after: 1 day
PR: 289097
Reviewed by: cperciva, jilles, bapt, emaste
Differential Revision: https://reviews.freebsd.org/D52161