osdc: remove pypi-cache and cache-enforcer from meta-prod-aws-ue1 (#848)

## Summary

Removes the `pypi-cache` and `cache-enforcer` modules from
`meta-prod-aws-ue1` in `osdc/clusters.yaml` — the only cluster that
actually enabled them:

- Drop `pypi-cache` and `cache-enforcer` from the cluster's `modules:`
list.
- Remove the `pypi_cache: { replicas: 10 }` per-cluster override.

`cache-enforcer` depends on `pypi-cache` (without the cache, runner pip
installs are blocked with no cache to serve them), so both are removed
together.

### Scope

Only `meta-prod-aws-ue1` had these modules enabled. The other meta
clusters (`meta-staging-aws-ue1/ue2`, `meta-prod-aws-uw1/ue2`) and the
`defaults:` block carry inert `pypi_cache:` config but never enabled the
module, so they are intentionally left untouched. The shared module
source (`osdc/modules/pypi-cache/`, `osdc/modules/cache-enforcer/`) is
also untouched.

## Operational note

Editing `clusters.yaml` only stops **future** deploys from managing
these modules; it does not uninstall already-deployed resources. To tear
down the live resources, an operator should run (after the PR lands):

```
just remove-module meta-prod-aws-ue1 cache-enforcer
just remove-module meta-prod-aws-ue1 pypi-cache
```

Removing `cache-enforcer` first avoids leaving runner traffic blocked
without a cache backend.

## Test plan

- `just lint` passes.
- `uv run scripts/cluster-config.py meta-prod-aws-ue1 has-module
pypi-cache|cache-enforcer` now reports both absent; the remaining
`modules` list resolves correctly.

Author: huydhn

osdc/clusters.yaml

@@ -405,17 +405,13 @@ clusters:
       github_secret_name: meta-prod-aws-ue1
       runner_name_prefix: "mt-"
       runner_group: "meta-prod-aws-ue1"
-    pypi_cache:
-      replicas: 10
     modules:
       - karpenter
       - arc
       - nodepools
       - arc-runners
       - keda
       - buildkit
-      - pypi-cache
-      - cache-enforcer
       - zombie-cleanup
       - harbor-cache-recovery
       - monitoring