[feature/extension-manager] Remove the ext_active index for lack of specificity

PHPBB3-10323

phpBB/develop/create_schema_files.php

@@ -1038,7 +1038,6 @@ function get_schema_struct()
 		),
 		'KEYS'			=> array(
 			'ext_name'				=> array('UNIQUE', 'ext_name'),
-			'ext_active'			=> array('INDEX', 'ext_active'),
 		),
 	);