Drop Toplevel::isOnScreen()

It's unused. Its replacement is Toplevel::isOnOutput().

src/toplevel.cpp

@@ -415,11 +415,6 @@ qreal Toplevel::bufferScale() const
     return surface() ? surface()->bufferScale() : 1;
 }
 
-bool Toplevel::isOnScreen(int screen) const
-{
-    return screens()->geometry(screen).intersects(frameGeometry());
-}
-
 bool Toplevel::isOnActiveOutput() const
 {
     return isOnOutput(workspace()->activeOutput());

src/toplevel.h

@@ -341,7 +341,6 @@ public:
     int y() const;
     int width() const;
     int height() const;
-    bool isOnScreen(int screen) const;   // true if it's at least partially there
     bool isOnOutput(AbstractOutput *output) const;
     bool isOnActiveOutput() const;
     int screen() const; // the screen where the center is