[feature] complete drop index stmt syntax with MySQL 8.0

[hustjieke]

In 8.0, the drop index syntax:

DROP INDEX index_name ON tbl_name
    [algorithm_option | lock_option] ...

algorithm_option:
    ALGORITHM [=] {DEFAULT | INPLACE | COPY}

lock_option:
    LOCK [=] {DEFAULT | NONE | SHARED | EXCLUSIVE}

radon now support:

DROP INDEX index_name ON table_name

radon should add options after stmt.