ARM: shmobile: koelsch: Remove legacy C board code

All features supported by the Koelsch legacy C board code are now
supported by the multiplatform code, it's thus time to say bye to the
legacy code. Nobody should miss it.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>