We don't support MySQL 5.6 since Moodle 3.11 so we can get rid of this hack in our unit test bootstrap.

https://bugs.mysql.com/bug.php?id=69882

It was fixed in:

• MySQL: Fixed as of 5.6.16 and 5.7.4, and here's the changelog entry:
• MariaDB 10.0.11 which merged 5.6.16 in. https://mariadb.com/kb/en/mariadb-10011-changelog/

So, TLDR:

• We can remove the mariadb hack from all branches (Moodle 3.9 already requires MariaDB 10.2.29).
• The MySQL 5.6 hack (<5.6.16) is only needed in the Moodle 3.9.x branch (later branches already require MySQL 5.7)
• The MySQL 5.7 hack (< 5.7.4) is needed for 39, 311, 400 and 401 (later branches already require MySQL 8).
• No hack is needed for Moodle 4.2 and up, complete removal.