openvpn: Deleted double entries for TLSAUTH and DAUTH.

Also drop remaining if clauses for Engines.
openvpn: Drop unused code from cgi file.

Deleted the following unused functions:

* checkportfw
* checkportoverlap
* checkportinc
* disallowreserved
openvpn: Changed directioning and added additional generation for ta.key.

Deleted the direction parameter 0 and 1 in ta.key directive for
compatibility purposes.
Added the ta.key generation also in PKI build process.
Replaced the ta.key to /certs instead of /ca and adapted the
apropriate paths.
Re-add missing language string "DNS Servers".