Drop no_frame flag from sdl_display_init argument list, use a global
variable instead.  This is temporary until -no-frame support is dropped
altogether when we remove sdl1 support.

Remove any traces of noframe from sdl2 code.  It is just dead code as
sdl2 doesn't support the SDL_NOFRAME window flag any more.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Message-id: 20180115154855.30850-3-kraxel@redhat.com