The only case which does not override mp_input_default_key_func in
mp_input_add_key_fd() is fd 0, but that is later special-cased not to
use the input function at all. Remove the useless default function.
git-svn-id: svn://svn.mplayerhq.hu/mplayer/trunk@24148 b3059339-0415-0410-9bf9-f77b7e298cf2