console: purge curses bits from console.h

Handle the translation from vga chars to curses chars in curses_update()
instead of console_write_ch().  Purge any curses support bits from
ui/console.h include file.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Message-id: 20170927103811.19249-1-kraxel@redhat.com