QGtkIntegration: Remove X display hack

Don't try pretend to be X when not really X. This is probably going to
break in very scary ways, and the one usecase for it (Krita) hardcodes
xcb at present anyway.

src/qgtkintegration.cpp

@@ -226,14 +226,11 @@ void *QGtkIntegration::nativeResourceForIntegration(const QByteArray &resource)
             qWarning() << "XCB connection requested; this is experimental, and may not work well.";
             xcb_warned = true;
         }
-        Display *dpy;
+        Display *dpy = nullptr;
         if (GDK_IS_X11_DISPLAY(m_display)) {
             dpy = gdk_x11_display_get_xdisplay(m_display);
         } else {
-            if (!m_xDisplay) {
-                m_xDisplay = XOpenDisplay(nullptr);
-            }
-            dpy = (Display*)m_xDisplay;
+            qWarning() << "Can't get XCB connection, GDK_BACKEND is not X11.";
         }
         xcb_connection_t *conn = XGetXCBConnection(dpy);
         result = reinterpret_cast<void*>(conn);
@@ -245,14 +242,11 @@ void *QGtkIntegration::nativeResourceForIntegration(const QByteArray &resource)
             qWarning() << "X11 display handle; this is experimental, and may not work well.";
             x11_warned = true;
         }
-        Display *dpy;
+        Display *dpy = nullptr;
         if (GDK_IS_X11_DISPLAY(m_display)) {
             dpy = gdk_x11_display_get_xdisplay(m_display);
         } else {
-            if (!m_xDisplay) {
-                m_xDisplay = XOpenDisplay(nullptr);
-            }
-            dpy = (Display*)m_xDisplay;
+            qWarning() << "Can't get XCB connection, GDK_BACKEND is not X11.";
         }
         result = reinterpret_cast<void*>(dpy);
 #endif

src/qgtkintegration.h

@@ -38,7 +38,6 @@
 #include <gdk/gdk.h>
 
 typedef void *EGLDisplay;
-typedef void *XDisplay;;
 
 QT_BEGIN_NAMESPACE
 
@@ -90,7 +89,6 @@ class QGtkIntegration : public QPlatformIntegration, public QPlatformNativeInter
     QGtkClipboard *m_clipboard = nullptr;
 
     EGLDisplay m_eglDisplay; // non-null for wayland platforms
-    XDisplay m_xDisplay = nullptr; // used in the native platform interface
 };
 
 QT_END_NAMESPACE