A couple years back we rolled out a full update of VP9 video transcodes for all files (T200747), but kept the VP8 configuration live to ensure continuity until the batch encodes finished (which took a couple months). This is long since finished, so disabling them will free up CPU time on scalers and space on file storage.
A single WebM VP8/Vorbis transcode should be kept for backwards compatibility with very old browsers, probably 360p (640x360 for 16:9). I'll prep a patch to mediawiki-config, and can run the batch-deletion process myself.