Fix regression in EglOnXBackend caused by b1914b4b2c

The ctor used by kwin_x11 still had the call to init which is now
performed by SceneOpenGL. This means init was performed twice
ultimately hitting an assert when creating the overlay window.

eglonxbackend.cpp

@@ -46,7 +46,6 @@ EglOnXBackend::EglOnXBackend()
     , m_rootWindow(rootWindow())
     , m_x11ScreenNumber(kwinApp()->x11ScreenNumber())
 {
-    init();
     // Egl is always direct rendering
     setIsDirectRendering(true);
 }