Rename files to reflect ReferencePolicy -> ReferenceGrant

[nathancoleman]

These were missed in #1179

What type of PR is this?

/kind cleanup
/kind failing-test

What this PR does / why we need it:
Some file renames were missed. The only functional impact today is that some conformance tests won't run because they reference ...reference-grant.yaml for resources to create, but those files are still named ...reference-policy.yaml.

Which issue(s) this PR fixes:

Fixes #

Does this PR introduce a user-facing change?:

NONE

[k8s-ci-robot]

Hi @nathancoleman. Thanks for your PR.

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[robscott]

/ok-to-test

[robscott]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: nathancoleman, robscott

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