Fix a few config parameters after the Paxos improvements commit

After committing the Paxos improvements, it was identified that the following configuration parameters need additional work:

• repair_request_timeout_in_ms - can be removed
• paxos_auto_repair_threshold_mb - I think it can be also removed; to be confirmed with the author

Discussed a bit in Slack and on this PR - https://github.com/apache/cassandra/commit/d2923275e360a1ee9db498e748c269f701bb3a8b