ivi-shell: remove configured signal from ivi-layout

Now that ivi-layout calls directly into ivi-shell.c, this signal is no
longer used. Remove it.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Emre Ucan <eucan@de.adit-jv.com>