Does SQL Server 2016 still contain sqlmaint.exe?
Microsoft documentation mentions they're removing it, it says "Next Version" but i assume this was written for a previous version. They advise to use maintenance plans in the future.

Microsoft Documentation for sqlmaint

Edit: Last update on that article was 03/14/2017. But given all the examples point to it being originally written with SQL Server 2008 in some and edited with later versions as examples (it's all over the place to be honest), it's probably safe to say the note at the top is wrong and it's actually removed already.