Extended paper - should I keep someone who virtually had no contribution?
In all journals (CS/AI) I’ve worked with you need all authors of the conference paper(s) on which the journal version is based on to agree on the author list in the journal version. Some editors will just not allow a paper to be accepted before explicit consent has been obtained. 

It is also unfair to an extent towards this professor. Think about this professor’s perspective: they may believe their contribution was much greater than just some textual edits, and once they realize that you submitted a version without their knowledge or consent, they’ll just email the editor and the paper will not go through to publication before it’s all sorted out.

I suggest you email the professor, tell them your plan, and whether they’d like to still be written as a coauthor. Most people would get the hint. Even if they’d still want to be included then there’s not much you can do about it: you should have established authorship in the conference version.