From @Anomie on https://gerrit.wikimedia.org/r/#/c/378261/:
update.php fails on a fresh install without this patch, with a DBQueryError exception for the error "42710 ERROR: enum label "3D" already exists". I don't know if the installer runs update.php or not.
update.php works fine on wikis created prior to Id6bfe8d2, as in that case the update is needed and runs successfully, and then the updater remembers that it has done that patch (in the updatelog table) and doesn't repeat it on subsequent runs.