Drop Application::isClosingX11Connection()

It's unused.

src/main.h

@@ -190,14 +190,6 @@ public:
         return m_defaultScreen;
     }
 
-    /**
-     * Returns @c true if we're in the middle of destroying the X11 connection.
-     */
-    bool isClosingX11Connection() const
-    {
-        return m_isClosingX11Connection;
-    }
-
 #if KWIN_BUILD_ACTIVITIES
     bool usesKActivities() const
     {
@@ -286,10 +278,6 @@ protected:
     {
         m_terminating = true;
     }
-    void setClosingX11Connection(bool set)
-    {
-        m_isClosingX11Connection = set;
-    }
 
 protected:
     static int crashes;
@@ -311,7 +299,6 @@ private:
 #endif
     Platform *m_platform = nullptr;
     bool m_terminating = false;
-    bool m_isClosingX11Connection = false;
 };
 
 inline static Application *kwinApp()

src/xwayland/xwayland.cpp

@@ -152,7 +152,6 @@ void Xwayland::uninstallSocketNotifier()
 void Xwayland::handleXwaylandFinished()
 {
     disconnect(kwinApp()->platform(), &Platform::primaryOutputChanged, this, &Xwayland::updatePrimary);
-    m_app->setClosingX11Connection(true);
 
     delete m_xrandrEventsFilter;
     m_xrandrEventsFilter = nullptr;
@@ -165,8 +164,6 @@ void Xwayland::handleXwaylandFinished()
     m_selectionOwner.reset();
 
     destroyX11Connection();
-
-    m_app->setClosingX11Connection(false);
 }
 
 void Xwayland::handleXwaylandReady()