chore: remove duplicated metric to count the number of processed records

[javiermolinar]

What this PR does:

I noticed we have three different metrics that measure the same:

tempo_distributor_produce_records_total
tempo_distributor_produce_requests_total
tempo_distributor_kafka_appends_total

This PR removes the tempo_distributor_kafka_appends_total.
There are already two other metrics that measure the same:

tempo_distributor_produce_requests_total and tempo_distributor_produce_failures_total

tempo_distributor_produce_records_total is added by kprom here:

tempo/pkg/ingest/writer_client.go

Line 34 in b8f58a8

kprom.FetchAndProduceDetail(kprom.Batches, kprom.Records, kprom.CompressedBytes, kprom.UncompressedBytes))

tempo_distributor_produce_requests_total is named requests to avoid a name conflict with the above one.

Question: Should we keep both?. Kprom includes a lot of metrics, some of them overlaps with another ones defined by us which on the other hand are tunable and easier to find.

Which issue(s) this PR fixes:
Fixes #

Checklist

• Tests updated
• Documentation added
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]