security/softether5: deprecate UNLOCK option

RADIUS authentication is available by default config now.

It turned out the restriction is applied only to the original binaries
and source codes. Anyone except Daiyuu Nobori can remove the restriction.

[1] https://github.com/SoftEtherVPN/SoftEtherVPN/blob/485a592/src/Cedar/Server.c#L10611-L10642