spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD

The SPDX folks have obsoleted the BSD-2-Clause-FreeBSD identifier. Catch
up to that fact and revert to their recommended match of BSD-2-Clause.

Discussed with: pfg
MFC After: 3 days
Sponsored by: Netflix

rc: Start testing the rc(8) framework (beginning with *_oomprotect)

This change adds 2 tests to make sure that the *_oomprotect variable
sets the protection against OOM killer properly within rc(8) scripts.

This is also adding the first tests for the rc(8) framework. More tests
will be added as we go.

PR: 256148
Approved by: des
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D35745