Remove "Converger" metrics from the metrics docs.

[andrew-edgar]

Since the converger is no longer a component and there is nothing emitting those metrics should those not be removed from the doc?

[cf-gitbot]

We have created an issue in Pivotal Tracker to manage this:

https://www.pivotaltracker.com/story/show/139935223

The labels on this github issue will be updated when the story is started.

[emalm]

Thanks, @andrew-edgar. Coincidentally, https://www.pivotaltracker.com/story/show/137740383 recently made it to the top of the Diego backlog, so that's done in that story.

Best,
Eric