Revisit (rewrite or remove) rate limiting

[kevinbader]

Currently, the code around rate limiting is basically dead: inactive by default, with config values in the ops-guide marked as deprecated. We need to decide whether we need this feature. If we do, we need to check whether we can re-use existing code; otherwise, we should get rid of it.

[jakobwgnr]

As discussed with @kevinbader and @mmacai the Rate limiting won't be used anymore and should be removed from the code.