There is no way to remove ceramic tile and end up with a surface smooth enough for vinyl. At best, you have to bring in a grinder and create an awful mess. Still probably end up putting some 1/4" subfloor. You could put some 1/8 luan directly over the existing ceramic. I would remove the toilet and build up the flange, but it is definitely possible to cut the vinyl behind the bowl and make a good install that way.