code: public function dropCheck($name, $table)
      {
          return 'ALTER TABLE ' . $this->db->quoteTableName($table)
              . ' DROP CONSTRAINT ' . $this->db->quoteColumnName($name);
      }
docs: Creates a SQL command for dropping a check constraint.
  @param string $name the name of the check constraint to be dropped.
  The name will be properly quoted by the method.
  @param string $table the table whose check constraint is to be dropped.
  The name will be properly quoted by the method.
  @return string the SQL statement for dropping a check constraint.
  @since 2.0.13