meta-resin-odroid/conf/layer.conf: Remove obsolete u-boot reference
meta-resin-odroid/conf/layer.conf: Remove obsolete u-boot reference

We do not use u-boot version 2017.09 anymore so we remove the
preference to this version from layer.conf.

Signed-off-by: Florin Sarbu <3a837a37a2ac9072a088641ec330e0e5d5b86f4e@balena.io>

resin-os/resin-odroid