Cygwin: pty: Fix screen distortion after less for native apps again.

- Commit c4b060e3fe seems to be not
  enough. Moreover, it does not work as expected at all in Win10
  1809. This patch essentially reverts that commit and add another
  fix. After all, the cause of the problem was a race issue in
  switch_to_pcon_out flag. That is, this flag is set when native
  app starts, however, it is delayed by wait_pcon_fwd(). Since the
  flag is not set yet when less starts, the data which should go
  into the output_handle accidentally goes into output_handle_cyg.
  This patch fixes the problem more essentially for the cause of
  the problem than previous one.

winsup/cygwin/tty.h

@@ -105,7 +105,6 @@ private:
   pid_t pcon_pid;
   UINT term_code_page;
   bool need_redraw_screen;
-  HANDLE fwd_done;
   DWORD pcon_last_time;
   bool pcon_in_empty;
   bool req_transfer_input_to_pcon;