The http connection limit is for any HTTP operation and is independent
of the other connection limits. It should be set to a higher value than
the query limit. The difference between this and the query limit is it
will close out the connection immediately without any further
processing.
This is the equivalent of the `max_connections` option in PostgreSQL.
Also removes some unused config options from the cluster config.
Fixes#6559.
Jonathan A. Sternberg