Remove deprecated functions that were marked for removal per review:
- Remove GetPodsUsingPVC (replaced by GetPodsUsingPVCWithCache)
- Remove IsPVCDefaultToFSBackup (replaced by IsPVCDefaultToFSBackupWithCache)
- Remove associated tests for deprecated functions
- Add deprecation marker to NewVolumeHelperImpl
- Add deprecation marker to ShouldPerformSnapshotWithBackup
Signed-off-by: Shubham Pampattiwar <spampatt@redhat.com>