vt: Drop a no longer true comment.

Some guy went on a patching spree, adding 24-bit colour support all around:
https://gist.github.com/XVilka/8346728



Signed-off-by: Adam Borowski <kilobyte@angband.pl>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>