web: setup: simplify the setup wizard

The RAUC bundle based install method was not implemented yet and may just
as well be integrated into the main wizard flow, so we can just remove it.
While at it also get rid of the "Start Exploring" page, as it is somewhat
redundant.

Signed-off-by: Leonard Göhrs <l.goehrs@pengutronix.de>

Author: hnez