void addRegionToRestore(final RegionInfo hri) {
      if (regionsToRestore == null) {
        regionsToRestore = new LinkedList<>();
      }
      regionsToRestore.add(hri);
    }
Returns the list of regions removed during the on-disk restore. The caller is responsible to
remove the regions from META. e.g. MetaTableAccessor.deleteRegions(...)
@return the list of regions to remove from META
hbase-server/src/main/java/org/apache/hadoop/hbase/snapshot/RestoreSnapshotHelper.java