fix bug : full ddl sqls should not assign to extra field but data field

parse/src/test/java/com/alibaba/otter/canal/parse/inbound/mysql/tsdb/MemoryTableMeta_DDL_Test.java

@@ -6,9 +6,6 @@ import java.net.URL;
 import java.util.ArrayList;
 import java.util.List;
 
-import com.alibaba.druid.sql.repository.SchemaObject;
-import com.alibaba.druid.sql.repository.SchemaRepository;
-import com.alibaba.druid.util.JdbcConstants;
 import org.apache.commons.io.IOUtils;
 import org.apache.commons.lang.StringUtils;
 import org.junit.Assert;