remove the check for the existence of NFS files

[fusida]

after #3351, we find there are still many requests for nfs stats in some case.
through analysis and debugging, we found the FileExists function will cause manay unnecessary requests.
so we suggesst remove the check for the existence of NFS files and that reduced requests to nas significantly.

fix #3349
fix #3351

[k8s-ci-robot]

Hi @fusida. Thanks for your PR.

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[fusida]

@iwankgb PTAL, thanks a lot～

[iwankgb]

/ok-to-test