Add DROP INDEX support to DatabaseSqlite::replaceVars method

DROP INDEX is database-wide (and not table-specific) in SQLite,
so we need to add a rule in our MySQL to SQLite schema convert.

"DROP INDEX foo ON bar" becomes "DROP INDEX foo".

Change-Id: Ie10784d166ed5a7f6ea52cf4f3a812fb7878a744
Merge "Add DROP INDEX support to DatabaseSqlite::replaceVars method"