Stop trying to set the Platform in runtime specs
Stop trying to set the Platform in runtime specs

run: The latest version of runtime-spec dropped the Platform field, so
stop trying to set it when generating a configuration for a runtime.

Signed-off-by: Nalin Dahyabhai <nalin@redhat.com>

Closes: #201
Approved by: rhatdan

projectatomic/buildah,TomSweeneyRedHat/buildah,rhatdan/buildah,projectatomic/buildah,nalind/buildah,rhatdan/buildah,rhatdan/buildah,nalind/buildah,ipbabble/buildah,ipbabble/buildah,TomSweeneyRedHat/buildah,projectatomic/buildah,nalind/buildah-1,TomSweeneyRedHat/buildah,nalind/buildah-1,nalind/buildah-1