Revert pbsplash for now

I am not proposing this with the intent to stir controversy or discredit someone's work, but pbsplash has made anyone using a graphical display manager unable to boot into postmarketOS properly (See https://gitlab.com/postmarketOS/pmaports/-/issues/1960). I don't think this is an acceptable regression. To me it seems like needs more testing before it can be deployed widely.