Remove VolumeSnapshotClass from CSI B/R process.

[blackpiglet]

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Please add a summary of your change

Does your change fix a particular issue?

Fixes #9033

Please indicate you've done the following:

• Accepted the DCO. Commits without the DCO will delay acceptance.
• Created a changelog file (make new-changelog) or comment /kind changelog-not-required on this PR.
• Updated the corresponding documentation in site/content/docs/main.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 60.26%. Comparing base (554b04e) to head (0964365).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9431      +/-   ##
==========================================
+ Coverage   60.23%   60.26%   +0.02%     
==========================================
  Files         386      386              
  Lines       35937    35908      -29     
==========================================
- Hits        21648    21641       -7     
+ Misses      12715    12697      -18     
+ Partials     1574     1570       -4     

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[kaovilai]

Consider documenting

"When restoring to a different cluster, any VolumeSnapshotClass-specific parameters (e.g., AWS EBS Fast Snapshot Restore, GCP storage-locations) from the source cluster will not be preserved. Ensure your destination cluster's default VolumeSnapshotClass is configured appropriately for your workload requirements."

[blackpiglet]

Consider documenting

"When restoring to a different cluster, any VolumeSnapshotClass-specific parameters (e.g., AWS EBS Fast Snapshot Restore, GCP storage-locations) from the source cluster will not be preserved. Ensure your destination cluster's default VolumeSnapshotClass is configured appropriately for your workload requirements."

Restoring to a new cluster doesn't require a VolumeSnapshotClass to work.
Because the VolumeSnapshot and VolumeSnapshotContent are created from VolumeSnapshotClass, they already have the VolumeSnapshotClass's parameter in them, and Velero only needs to restore the backed-up VolumeSnapshot and VolumeSnapshotContent; no dynamic creation is required.

As a result, the restore can work even without any VolumeSnapshotClass existing in the cluster.