…rmint#2804) (tendermint#2813)

Followup to tendermint#2792 which closed tendermint#2771.

tendermint#2792 does not handle the case where Start is never called. If Start is
not called, Stop returns an error, thus with tendermint#2792's implementation the
only way to ensure that PingPongLatencyTimer is cleaned up is to call
Start and Stop, even when not using any of the features provided by
Start (i.e. events).

This PR moves initialization of PingPongLatencyTimer into OnStart so
that it is only initialized if it is going to be used. This PR also
moves cleanup of PingPongLatencyTimer into readRoutine's defer statement
to align it with other cleanup (i.e. closing the connection).

#### PR checklist

- [ ] Tests written/updated
- [ ] Changelog entry added in `.changelog` (we use
[unclog](https://github.com/informalsystems/unclog) to manage our
changelog)
- [ ] Updated relevant documentation (`docs/` or `spec/`) and code
comments
- [ ] Title follows the [Conventional
Commits](https://www.conventionalcommits.org/en/v1.0.0/) spec
<hr>This is an automatic backport of pull request tendermint#2804 done by
[Mergify](https://mergify.com).

Co-authored-by: Ethan Reesor <firelizzard@gmail.com>