Update database wants to drop db indexes... why?

Hi,
in one of my websites (Contao 3.5.3) the update database shows me that he wants to:

ALTER TABLE `tl_article` DROP INDEX `pid`;
ALTER TABLE `tl_calendar_events` DROP INDEX `pid`;
ALTER TABLE `tl_comments` DROP INDEX `source`;
ALTER TABLE `tl_comments` DROP INDEX `parent`;
ALTER TABLE `tl_comments_notify` DROP INDEX `source`;
ALTER TABLE `tl_comments_notify` DROP INDEX `parent`;
ALTER TABLE `tl_comments_notify` DROP INDEX `tokenConfirm`;
ALTER TABLE `tl_content` DROP INDEX `pid`;
ALTER TABLE `tl_faq` DROP INDEX `pid`;
ALTER TABLE `tl_news` DROP INDEX `pid`;
ALTER TABLE `tl_page` DROP INDEX `pid`;
ALTER TABLE `tl_page` DROP INDEX `type`;

Why?

Validate your installation with the Contao Check.

But I think that's normal. The indexes have changed in newer Contao versions.

Hm, yeah that's true. In Contao 3.5 the index has been changed to a combined index: https://github.com/contao/core/blob/...rticle.php#L43