Drop Toplevel::transparentRect()

It can be computed via other means (Toplevel::frameMargins()) and its
name is confusing. It specifies the inner decoration rect.

src/effects.cpp

@@ -1987,7 +1987,7 @@ void EffectWindowImpl::setSceneWindow(Scene::Window* w)
 
 QRect EffectWindowImpl::decorationInnerRect() const
 {
-    return toplevel->transparentRect();
+    return toplevel->rect() - toplevel->frameMargins();
 }
 
 QByteArray EffectWindowImpl::readProperty(long atom, long type, int format) const

src/scene.cpp

@@ -656,7 +656,8 @@ void Scene::Window::unreferencePreviousPixmap_helper(SurfaceItem *item)
 
 QRegion Scene::Window::decorationShape() const
 {
-    return QRegion(toplevel->rect()) - toplevel->transparentRect();
+    const QRect decorationInnerRect = toplevel->rect() - toplevel->frameMargins();
+    return QRegion(toplevel->rect()) - decorationInnerRect;
 }
 
 bool Scene::Window::isVisible() const

src/toplevel.h

@@ -362,7 +362,6 @@ public:
      * Returns a rectangle that the window occupies on the screen, including drop-shadows.
      */
     QRect visibleGeometry() const;
-    QRect transparentRect() const;
     virtual bool isClient() const;
     virtual bool isDeleted() const;
 
@@ -789,11 +788,6 @@ inline QRect Toplevel::rect() const
     return QRect(0, 0, width(), height());
 }
 
-inline QRect Toplevel::transparentRect() const
-{
-    return isShade() ? QRect() : QRect(clientPos(), clientSize());
-}
-
 inline bool Toplevel::readyForPainting() const
 {
     return ready_for_painting;