spdx: The BSD-2-Clause-NetBSD identifier is obsolete, drop -NetBSD
The SPDX folks have obsoleted the BSD-2-Clause-NetBSD 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
(cherry picked from commit b61a573019428cbdc38ed03be9ecd2482011ea66)