Tidy up now that minimum Qt6 version is 6.4

CMakeLists.txt

@@ -137,7 +137,7 @@ if (NOT APPLE)
             if (QT_MAJOR_VERSION STREQUAL "5")
                 find_package(Qt5X11Extras ${QT_REQUIRED_VERSION} REQUIRED NO_MODULE)
             else()
-                find_package(Qt${QT_MAJOR_VERSION} ${QT_REQUIRED_VERSION} CONFIG REQUIRED Gui) # qtx11extras_p.h for Qt6 < 6.2
+                find_package(Qt${QT_MAJOR_VERSION} ${QT_REQUIRED_VERSION} CONFIG REQUIRED Gui)
             endif()
             add_feature_info(ENABLE_X11 ${ENABLE_X11} "Enable use of X11")
         endif()

src/messagewindow.cpp

@@ -36,12 +36,10 @@
 #if ENABLE_X11
 #include <KWindowInfo>
 #include <netwm.h>
-#if QT_VERSION >= QT_VERSION_CHECK(6, 2, 0)
-#include <QGuiApplication>
-#elif QT_VERSION >= QT_VERSION_CHECK(6, 0, 0)
-#include <private/qtx11extras_p.h>
-#else
+#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
 #include <QX11Info>
+#else
+#include <QGuiApplication>
 #endif
 #endif
 #include <QTextBrowser>