private static boolean isDeleteColumnFamily(TableDescriptor originalDescriptor,
    TableDescriptor newDescriptor) {
    boolean result = false;
    final Set<byte[]> originalFamilies = originalDescriptor.getColumnFamilyNames();
    final Set<byte[]> newFamilies = newDescriptor.getColumnFamilyNames();
    for (byte[] familyName : originalFamilies) {
      if (!newFamilies.contains(familyName)) {
        result = true;
        break;
      }
    }
    return result;
  }
Find out whether all column families in unmodifiedTableDescriptor also exists in the
modifiedTableDescriptor.
@return True if we are deleting a column family.
hbase-server/src/main/java/org/apache/hadoop/hbase/master/procedure/ModifyTableProcedure.java