db/DatabaseListener: pass URI to OnDatabaseSongRemoved()

There's no point in passing a LightSong reference here; the callee is
interested only in the URI.

src/db/DatabaseListener.hxx

@@ -40,7 +40,7 @@ public:
 	 * During database update, a song is about to be removed from
 	 * the database because the file has disappeared.
 	 */
-	virtual void OnDatabaseSongRemoved(const LightSong &song) = 0;
+	virtual void OnDatabaseSongRemoved(const char *uri) = 0;
 };
 
 #endif

src/db/update/Remove.cxx

@@ -39,10 +39,9 @@ UpdateRemoveService::RunDeferred()
 	{
 		const auto uri = removed_song->GetURI();
 		FormatDefault(update_domain, "removing %s", uri.c_str());
+		listener.OnDatabaseSongRemoved(uri.c_str());
 	}
 
-	listener.OnDatabaseSongRemoved(removed_song->Export());
-
 	/* clear "removed_song" and send signal to update thread */
 	remove_mutex.lock();
 	removed_song = nullptr;