@Override
  protected void doAlteration(Table table, Partition partition) throws HiveException {
    StorageDescriptor sd = getStorageDescriptor(table, partition);
    for (String key : desc.getProps().keySet()) {
      sd.getSerdeInfo().getParameters().remove(key);
    }
  }
Operation process of unsetting serde properties.
ql/src/java/org/apache/hadoop/hive/ql/ddl/table/storage/serde/AlterTableUnsetSerdePropsOperation.java