release: Remove not-NO_ROOT cases

We always use NO_ROOT for release artifact builds, so remove the
alternate code paths.

For the first step we set NO_ROOT unconditionally in cases that invoke
submakes, and turn NO_ROOT being unset into an error in lover-level
targets so that we can catch potential out-of-tree build scripts (or
missed in-tree cases) that expect to run not-NO_ROOT builds. The second
step will be to remove those entirely.

Reviewed by: cperciva
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D54179

(cherry picked from commit 54e006369c9aab4f3a22f026eb6924c0f9cafda8)