Changes

Migrate prow kubernetes jobs from `gcp-prow-ksyun` to `default` cluster (#4340)

Prow's default cluster is `default`. Jobs pinned to `gcp-prow-ksyun`
need to be migrated by dropping the `cluster` field and removing
dependencies on PVCs that don't exist in the default cluster.

## Changes

- **Remove `cluster: gcp-prow-ksyun`** from all affected jobs (7 files)
— omitting the field defaults to `default` cluster
- **Remove go mod cache dependencies** (env vars
`GO_PROXY`/`GOMODCACHE`, `gomod-cache` PVC volumeMounts/volumes) from
jobs in `tidb-binlog` and `tikv/pd`
- **Remove cargo cache PVC volumes** from `tikv/raft-engine` jobs where
volumeMounts were already commented out (orphaned declarations)
- **Remove cargo cache volumeMounts/volumes** from `tidb-engine-ext`
jobs (both `latest` and `release-6.1`)

## Pending image migrations (`hub.pingcap.net`)

The following jobs still reference internal `hub.pingcap.net` images
that need to be migrated to a public registry — marked with
`TODO(@wuhuizuo)`:

| File | Image |
|------|-------|
| `pingcap/tidb-engine-ext/latest-presubmits.yaml` |
`hub.pingcap.net/tiflash/tiflash-llvm-base:amd64` |
| `pingcap/tidb-engine-ext/release-6.1-latest-presubmits.yaml` |
`hub.pingcap.net/tiflash/tiflash-llvm-base:amd64` |
| `pingcap/tidb-binlog/latest-presubmits.yaml` |
`hub.pingcap.net/jenkins/centos7_golang-1.21:latest`,
`hub.pingcap.net/jenkins/zookeeper`, `hub.pingcap.net/jenkins/kafka` |
| `tikv/pd/release-6.1-presubmits.yaml` |
`hub.pingcap.net/ee/ci/base:v20230803-go1.19.12` |

<!-- START COPILOT ORIGINAL PROMPT -->



<details>

<summary>Original prompt</summary>

> 
> ----
> 
> *This section details on the original issue you should resolve*
> 
> <issue_title>Migrate prow kubernetes type jobs which run on cluster
`gcp-prow-ksyun` to `default` cluster</issue_title>
> <issue_description>prow job default cluster is `default`, so when we
migrate them, we can just delete the `cluster` field in prow job. And
some additional changes we need to make:
> 
> 1. when the job use go build or go mod cache env vars and volume and
volume mounts, please delete it.
> 2. when use images from hub.pingcap.net, your should add a task item
in the pull request description and assign the pr to @wuhuizuo and add
label "help wanted" to request help.
> 
> </issue_description>
> 
> ## Comments on the Issue (you are @copilot in this section)
> 
> <comments>
> </comments>
> 


</details>



<!-- START COPILOT CODING AGENT SUFFIX -->

- Fixes PingCAP-QE/ci#4339

<!-- START COPILOT CODING AGENT TIPS -->
---

🔒 GitHub Advanced Security automatically protects Copilot coding agent
pull requests. You can protect all pull requests by enabling Advanced
Security for your repositories. [Learn more about Advanced
Security.](https://gh.io/cca-advanced-security)

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: wuhuizuo <2574558+wuhuizuo@users.noreply.github.com>
 (commit: 582f4a9)