Usage:
$smcFunc['db_remove_index'](table_name, index_name, parameters, error)
Description: This function removes a index.
Parameters:
- table_name (string) the name of an existing table
- index_name (string) the name of the index to remove.
- parameters (array) deprecated as of 2.0 RC3, leave empty
- error (string) deprecated as of 2.0 RC3, leave empty
Return: (bool) true if the index is successfully removed, false if the index is not found.