Simplify Toplevel::isOnDesktop() and Toplevel::isOnAllDesktops()

Wayland- and X11-specific code paths are not needed.

If the window is on all virtual desktops, Toplevel::desktops() will be
an empty list.

If the window is on a particular virtual desktop, Toplevel::desktops()
will contain that desktop. On X11, the desktops list can have at most
only one item.

src/toplevel.cpp

@@ -693,11 +693,7 @@ QMargins Toplevel::frameMargins() const
 
 bool Toplevel::isOnDesktop(int d) const
 {
-    return (kwinApp()->operationMode() == Application::OperationModeWaylandOnly ||
-            kwinApp()->operationMode() == Application::OperationModeXwayland
-            ? desktops().contains(VirtualDesktopManager::self()->desktopForX11Id(d))
-            : desktop() == d
-           ) || isOnAllDesktops();
+    return isOnAllDesktops() || desktops().contains(VirtualDesktopManager::self()->desktopForX11Id(d));
 }
 
 bool Toplevel::isOnCurrentDesktop() const

src/toplevel.h

@@ -923,12 +923,7 @@ const EffectWindowImpl* Toplevel::effectWindow() const
 
 inline bool Toplevel::isOnAllDesktops() const
 {
-    return kwinApp()->operationMode() == Application::OperationModeWaylandOnly ||
-           kwinApp()->operationMode() == Application::OperationModeXwayland
-        //Wayland
-        ? desktops().isEmpty()
-        //X11
-        : desktop() == NET::OnAllDesktops;
+    return desktops().isEmpty();
 }
 
 inline bool Toplevel::isOnAllActivities() const