Also fail with DISPLAY with wayland platform plugin

QtWebEngine spews errors at us, and while it seems to work with Weston for some
reason (despite errors logged), it doesn't with sway.

qutebrowser/misc/backendproblem.py

@@ -174,10 +174,6 @@ def _handle_nouveau_graphics():
 def _handle_wayland():
     if QApplication.instance().platformName() not in ['wayland', 'wayland-egl']:
         return
-    if os.environ.get('DISPLAY'):
-        # When DISPLAY is set but with the wayland/wayland-egl platform plugin,
-        # QtWebEngine will do the right hting.
-        return
 
     _show_dialog(
         backend=usertypes.Backend.QtWebEngine,