security/openvpn-devel: options cleanup

• Drop TUNNELBLICK option and patch, which fails PATCH and if your force it, build. security/openvpn removed the option earlier this year. Drop pkg-help along with it
• Exclude DCO-option on FreeBSD 12 and 13. It requires FreeBSD 14 kernel features, and FreeBSD 11 and older are no longer supported.

Approved by: portmgr (blanket)