Diviner: Remove line about MySQL issues with indexes for tuple search master
Summary: Older MySQL versions had performance issues in query optimization for tuple comparisons in an IN clause. These issues were mostly fixed for MySQL 5.6; see https://bugs.mysql.com/bug.php?id=31188 While there are still some issues (e.g. https://bugs.mysql.com/bug.php?id=115190), nowadays tuple search index usage is generally supported. Phorge requires MySQL 8 since rP555fb3a8 / T16107. So this sentence is now moot. Test Plan: * Search the interwebs * Run `./bin/diviner generate`, read http://phorge.localhost/book/contrib/article/database/ Reviewers: O1 Blessed Committers, valerio.bozzolan Reviewed By: O1 Blessed Committers, valerio.bozzolan Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno Differential Revision: https://we.phorge.it/D26472