Remove redundant suffix from TorrentHandle class

Originally, it was just a wrapper for libtorrent::torrent_handle class, so it mimicked its name.
It was then transformed into a more complex aggregate, but the name was retained (just by inertia).
Unlike libtorrent::torrent_handle class in whose name "handle" means the pattern used,
it does not matter for qBittorrent classes and just eats up space in the source code.

src/gui/properties/trackerlistwidget.h

@@ -35,7 +35,7 @@ class PropertiesWidget;
 
 namespace BitTorrent
 {
-    class TorrentHandle;
+    class Torrent;
 }
 
 class TrackerListWidget : public QTreeWidget
@@ -70,7 +70,7 @@ public slots:
     void moveSelectionDown();
 
     void clear();
-    void loadStickyItems(const BitTorrent::TorrentHandle *torrent);
+    void loadStickyItems(const BitTorrent::Torrent *torrent);
     void loadTrackers();
     void askForTrackers();
     void copyTrackerUrl();