[ozone/wayland] Remove outdated comment.

Nothing special, just doing some garderning.

TBR=rjkroege@chromium.org

Bug: 859012
Change-Id: I2f750bbf2438521109b48be5932c74f93a80dc35
Reviewed-on: https://chromium-review.googlesource.com/1254263Reviewed-by: Maksim Sisov <msisov@igalia.com>
Commit-Queue: Maksim Sisov <msisov@igalia.com>
Cr-Commit-Position: refs/heads/master@{#595444}

ui/ozone/platform/wayland/gpu/gbm_surfaceless_wayland.cc

@@ -59,8 +59,6 @@ bool GbmSurfacelessWayland::IsOffscreen() {
 }
 
 bool GbmSurfacelessWayland::SupportsPresentationCallback() {
-  // TODO(msisov): enable a real presentation callback for wayland. For now, we
-  // just blindly say it was successful. https://crbug.com/859012.
   return true;
 }