code: public function dropIndex($name, $table)
      {
          $time = $this->beginCommand("drop index $name on $table");
          $this->db->createCommand()->dropIndex($name, $table)->execute();
          $this->endCommand($time);
      }
docs: Builds and executes a SQL statement for dropping an index.
  @param string $name the name of the index to be dropped. The name will be properly quoted by the method.
  @param string $table the table whose index is to be dropped. The name will be properly quoted by the method.