void pruneNamespaceSnapshots(Multimap<TableName, String> snapshotsToComputeSize)
    throws IOException {
    Set<String> existingSnapshotEntries = QuotaTableUtil.getNamespaceSnapshots(conn);
    for (TableName tableName : snapshotsToComputeSize.keySet()) {
      existingSnapshotEntries.remove(tableName.getNamespaceAsString());
    }
    // here existingSnapshotEntries is left with the entries to be removed
    removeExistingNamespaceSnapshotSizes(existingSnapshotEntries);
  }
Removes the snapshot entries that are present in Quota table but not in snapshotsToComputeSize
@param snapshotsToComputeSize list of snapshots to be persisted
hbase-server/src/main/java/org/apache/hadoop/hbase/quotas/SnapshotQuotaObserverChore.java