Relocate Benchmarks

## Overview

This section is mostly redundant with Benchmark section in [Operations guide > Performance](https://etcd.io/docs/v3.5/op-guide/performance/). Move any non-redundant info to the Performance section in the Operations Guide.

Remove old benchmarks if they're no longer needed.

Audience: The user role to which the task most applies, probably either Developer or Operator.

Type: Conceptual and Reference

The existing documentation might contain helpful source material that you can pull into this doc change. See recommendations for the existing (at the time of the CNCF tech doc analysis) etcd technical documentation pages:
https://github.com/cncf/techdocs/blob/main/assessments/0010-etcd/etcd-implementation.md/#general-reorganization

## 🎤 Context

This issue tracks recommended changes resulting from an analysis of the etcd documentation commissioned by CNCF. The analysis and supporting documents are here: https://github.com/cncf/techdocs/tree/main/assessments/0010-etcd/

## ✌️ Possible Implementation

Related material in the current doc:
- https://etcd.io/docs/v3.5/benchmarks/
- https://etcd.io/docs/v3.5/op-guide/performance/

Suggested changes:

Consolidate into the Performance section in the Operations Guide.

Remove old benchmarks.