There seems to be not too much call for super low resolutions; the patch for T312152 removes the 120p and 180p transcodes, so 240p is now the smallest size video output.
These files should be deleted to free space after it is deployed; that can be done with a call to requeueTranscodes.php like this:
php extensions/TimedMediaHandler/maintenance/requeueTranscodes.php --key=120p.vp9.webm php extensions/TimedMediaHandler/maintenance/requeueTranscodes.php --key=180p.vp9.webm
but on all wikis :D