wayland: always set refresh in presentation feedback

Currently, when VRR is enabled, the refresh in wayland presentation feedback is overriden to 0. This may have been done because of this quote from https://wayland.app/protocols/presentation-time#wp_presentation_feedback:event:presented

If the output does not have a constant refresh rate, explicit video mode switches excluded, then the refresh argument must be zero.

However, this breaks applications that rely on a non-zero refresh to accurately handle high refresh rates (e.g. chromium). Always setting refresh fixes this. This is also the behaviour of Sway (wlroots).