chore: use deprecated attribute on updateChannelC()

Author: DeepDiver1975

src/gui/updater/updater.cpp

@@ -34,11 +34,14 @@ namespace OCC {
 
 Q_LOGGING_CATEGORY(lcUpdater, "gui.updater", QtInfoMsg)
 
+[[deprecated("updateChannel is no longer supported. the key will be removed in 8.0")]]
+const QString updateChannelC() { return QStringLiteral("updateChannel"); }
+
 QString updateChannel()
 {
     // remove deprecated updateChannel setting once we hit 8.0
     auto settings = ConfigFile::makeQSettings();
-    QString updateChannelKey = "updateChannel";
+    QString updateChannelKey = updateChannelC();
     /*
     if (settings.contains(updateChannelKey)) {
         settings.remove(updateChannelKey);

src/libsync/configfile.cpp

@@ -59,8 +59,6 @@ const QString optionalDesktopNotificationsC()
 }
 const QString skipUpdateCheckC() { return QStringLiteral("skipUpdateCheck"); }
 const QString updateCheckIntervalC() { return QStringLiteral("updateCheckInterval"); }
-// deprecated - will be removed in 8.0
-// const QString updateChannelC() { return QStringLiteral("updateChannel"); }
 const QString uiLanguageC() { return QStringLiteral("uiLanguage"); }
 const QString geometryC() { return QStringLiteral("geometry"); }
 const QString timeoutC() { return QStringLiteral("timeout"); }