Traditionally, swap space is configured in /etc/fstab. It can be turned off with „swapoff -a“ (removes all swap devices).
Enter systemd (on Ubuntu 16.04): „swapoff -a“ turns of the swap – but only for 30 seconds. If you want to deactivate your swap „more permanently“, uncomment the swap part of /etc/fstab. You think you’re done? Think again, because „systemd knows best“ and goes ahead and reactivates all swap partitions (as it seems, that are on the same disc as /, didn’t test that yet) regardless your settings in fstab.
Given enough time, systemd rants are a good place to learn about non-expected systemd behaviour.