Clean up unused vars and types

[ialidzhikov]

/kind cleanup

All occurrences reported by the unused linter of golangci-lint.

Does this PR introduce a user-facing change?:

NONE

[k8s-ci-robot]

Hi @ialidzhikov. Thanks for your PR.

I'm waiting for a kubernetes-csi member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[Jiawei0227]

/ok-to-test
/lgtm

[ialidzhikov]

/retest

[Jiawei0227]

/lgtm
/approve

[msau42]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ialidzhikov, Jiawei0227, msau42

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