Co-authorship for a revised but relatively new article?
In this particular case, I would not change the authorship for the revised version (unless there are better reasons than what you have communicated).

You must not forget to keep your personal relations oiled. If you re-submit this article as a single-author paper, i.e. remove your supervisor, your relation to them would certainly not be helped. In the future, it may be important/useful to have that relation intact and well working for ongoing/future collaborations.

Moreover, by having them as co-author they are somewhat in your debt (which cannot be a bad thing) and may return the favor by adding you to one of their papers, even if you contributed as little as they did to yours.