spdx: The BSD-3-Clause-FreeBSD identifier never was, drop -FreeBSD
There never was a BSD-3-Clause-FreeBSD SPDX identifier. Replace it
with BSD-3-Clause.
Discussed with: pfg
MFC After: 3 days
Sponsored by: Netflix
(cherry picked from commit eb8f887758f31f605829c995ce71a627dec0838a)