Remove term_key, which was intended to handle function keys in a cross-

platform manner, but which nothing ever called.  It thus served only to
trap up the unwary.  The live function key handling code lives in the
frontends, i.e. window.c on Windows and gtkwin.c on Unix.

git-svn-id: svn://svn.tartarus.org/sgt/putty@9579 cda61777-01e9-0310-a592-d414129be87e