Drop Qt 5 support

Qt 6 has been available for almost 4 years. Qt 5 is no longer officially supported by Qt for opensource, it's time to drop Qt 5.

src/spotify/spotifyfavoriterequest.cpp

@@ -249,11 +249,7 @@ void SpotifyFavoriteRequest::RemoveFavoritesRequest(const FavoriteType type, con
     url.setQuery(url_query);
   }
   QNetworkRequest req(url);
-#if QT_VERSION >= QT_VERSION_CHECK(5, 9, 0)
   req.setAttribute(QNetworkRequest::RedirectPolicyAttribute, QNetworkRequest::NoLessSafeRedirectPolicy);
-#else
-  req.setAttribute(QNetworkRequest::FollowRedirectsAttribute, true);
-#endif
   req.setHeader(QNetworkRequest::ContentTypeHeader, QStringLiteral("application/x-www-form-urlencoded"));
   if (!access_token().isEmpty()) req.setRawHeader("authorization", "Bearer " + access_token().toUtf8());
   QNetworkReply *reply = nullptr;