task(auth-server): Don't report retryAfter to statsd on customs check events

[dschom]

Because

• We don't want to send values with high cardinality to stats

This pull request

• Ensures retryAfter isn't sent

Issue that this pull request solves

Closes: FXA-11492

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[chenba]

Thanks, Dan.

For anyone following along, we already configured Telegraf to ignore the 'retryAfter' tag. It was necessary to stablise the service.