Command - undo

- Migrated handleUndo to CmdUndo.

src/commands/CmdHelp.cpp

@@ -103,10 +103,6 @@ int CmdHelp::execute (const std::string&, std::string& output)
   view.set (row, 1, "task ID");
   view.set (row, 2, "Specifying an ID without a command invokes the 'info' command.");
 
-  row = view.addRow ();
-  view.set (row, 1, "task undo");
-  view.set (row, 2, "Reverts the most recent action.");
-
   row = view.addRow ();
   view.set (row, 1, "task delete ID");
   view.set (row, 2, "Deletes the specified task.");