Remove a mysterious GTK size-request tweak.

Remove a mysterious GTK size-request tweak.

In shortcut_add(), when we add an underlined letter to a GtkLabel, we
were fetching the label's height before changing its text, and
restoring it afterwards. I've no idea why - I can see no difference
with and without the code.

That code's been there since 2003 without explanation. My best guess
is that it was working around a GTK bug of the day, but since no
difference is visible even in current GTK1, I think I'm just going to
remove it. If any problems show up later, I can put it back, with an
actual comment!