Remove unnecessary call to newsym() in fov.cc

Remove unnecessary call to newsym() in fov.cc

As part of the general crusade to stop game logic directly calling into
display-nc.cc (so that notify-local-tty.cc and display-nc.cc can be replaced
with something that has a completely different interaction paradigm e.g. a
network client), the call to newsym() in fov.cc has been removed.

It was, in any event, superfluous because the only call to compute_fov()
was immediately followed by a call to touch_back_buffer().