BREAKING CHANGE: drop custom port feature

This feature is totally nonsense, you should just use your .ssh/config
to declare custom things to custom host. This created problems
because it was difficult to DO NOT specify a port, and without
hardcoding a port 22.

So, ssh_config should do this job, and we should not try to interact
with rsync internals and with SSH internals from this script.

Example configuration:

Host example.com
    Port 1234

That is everything you need.