citra-qt: Trim recently used files list to size when insterting new item

Even though they weren't visible in the UI, old entries would never be
removed from the list and would be stored in the config file across
sessions.

src/citra_qt/main.cpp

@@ -297,6 +297,10 @@ void GMainWindow::StoreRecentFile(const QString& filename)
     QStringList recent_files = settings.value("recentFiles").toStringList();
     recent_files.prepend(filename);
     recent_files.removeDuplicates();
+    while (recent_files.size() > max_recent_files_item) {
+        recent_files.removeLast();
+    }
+
     settings.setValue("recentFiles", recent_files);
 
     UpdateRecentFiles();