As discussed on https://bugzilla.wikimedia.org/show_bug.cgi?id=54604 , several of the icons – such as the PDF or IRC ones – are clearly useful. Several of them are also clearly useless, such as the HTTPS one. (I would suggest everybody to look at that discussion first to avoid repeating ourselves :) )
Personally I think the default external link one should be kept as well, the indication that this is an external resource is useful.