router: remove redundant dispatched_port_start/end configuration option from router config .toml

[matzf]

Follow up from #4344 (review)

The "dispatch ports" range is configured in the topology.json file, but can be overridden from the router configuration .toml.

Having two sources for one configuration value complicates things, both for the user and the implementation.
In this case, it appears that the override in the router configuration is used in an acceptance test only. Find a different way to run this acceptance test, and remove the flag from the configuration.