Interesting. I'd have expected that it's possible using localstorage but it isn't. So I don't think you can delete a save.
Imo the system save is way to crude for most cases anyway. It just indiscriminately saves everything down to the position of particles and such. This can be desired in some cases (and I do use it) but for a regular savefile I prefer using Localstorage and just save a handful of arrays/dictionaries. It just offers way more flexibility.