Cleanup: remove attributes no longer used after PR #1229

[prioux]

PR #1229 cleans up a bunch of stuff but leaves in the DB two attributes of the RemoteResource model that are no longer necessary:

• tunnel_mysql_port
• tunnel_actres_port

These attributes can be removed from the model.

We should wait a few weeks after production deployment of #1229 to make sure everything is OK, in case we have to revert back to the old mechanism.

Also: clean up/adjust all the CBRAIN installation instructions relative to these values.

[prioux]

Shoudl be combined with #1227

[MontrealSergiy]

seems ok yet I still find said attributes

tunnel_mysql_port tunnel_actres_port

in the generated docs /home/users/sboroday/cbrain/BrainPortal/doc/brainportal/RemoteResource.html