Fix TorrentFileGuard::setAutoRemove() recursion problem. Closes #6488.

The problem was created during Qt 4 drop, when FileGuard was promoted
from a member to a base class. The function was blindly changed.

src/base/torrentfileguard.h

@@ -60,7 +60,7 @@ public:
 
     /// marks the torrent file as loaded (added) into the BitTorrent::Session
     void markAsAddedToSession();
-    void setAutoRemove(bool remove);
+    using FileGuard::setAutoRemove;
 
     enum AutoDeleteMode     // do not change these names: they are stored in config file
     {