Remove PVCVolumeSnapshotRefList from VolumeGroupSnapshot API

[leonardoce]

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespaces from that line:

/kind api-change

/kind bug
/kind cleanup
/kind design
/kind documentation
/kind failing-test
/kind feature
/kind flake

What this PR does / why we need it:

This PR removes the PVCVolumeSnapshotRefList entry from the VolumeGroupSnapshot API. This is no longer needed since we now set persistentVolumeClaimName in the source of member VolumeSnapshots

Which issue(s) this PR fixes:

Fixes #1202

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

The `volumegroupsnapshot.status.pvcVolumeSnapshotRefList` field has been removed. VolumeShapshots members of a dynamically provisioned VolumeGroupSnapshot will have their `persistentVolumeClaimName` set, allowing the consumer to map the PVC being snapshotted with the corresponding snapshot.

[leonardoce]

/assign xing-yang

[xing-yang]

Can you add a note about the label in the PR description?

[xing-yang]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: leonardoce, xing-yang

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