This step can not be undone and should be planned carefully, both for private wikis and WMF.
The first caveat is that the location of the old PNG images is stored in the database only. Thus after the DB table is dropped, deleting the whole folder is the only remaining option to get rid of the images.
From the extension, everything is ready. All the code has been deleted T195847. cluster access is needed to decide if information is needed from the table to find the images of rendered mathematical expressions. Research that and if yes, search a path forward, if not, delete and/or archive.
- s1 (renamed the table on db2116 and db1089: T196055#5352527 and T196055#5384177)
- Remove the table from modules/role/files/mariadb/filtered_tables.txt: https://gerrit.wikimedia.org/r/#/c/529346/
- Remove the table from modules/profile/templates/labs/db/views/maintain-views.yaml: https://gerrit.wikimedia.org/r/#/c/operations/puppet/+/528724/ and run sudo /usr/local/sbin/maintain-views --all-databases --clean --replace-all on all labsdb hosts