Potential unused condition check in internal/xds/server/runner/runner.go

*Description*:
>Describe the issue.

There is a nil check in the
https://github.com/envoyproxy/gateway/blob/9036533c88ac786428ff6b173770875fc78c0de7/internal/xds/server/runner/runner.go#L137-L139

However, `r.cache` is initialized in https://github.com/envoyproxy/gateway/blob/9036533c88ac786428ff6b173770875fc78c0de7/internal/xds/server/runner/runner.go#L80 and `NewSnapshotCache` never returns a nil from it:
https://github.com/envoyproxy/gateway/blob/9036533c88ac786428ff6b173770875fc78c0de7/internal/xds/cache/snapshotcache.go#L108-L117

IMHO, the logger message is suspicious because the code around doesn't `init snapshot cache`. It could be a remnant of a previous refactor.

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