buildroot

infra: remove auto derivation of host dependencies

This feature consists in automatically deducing dependencies of a host
package from the dependencies of the target variant.

However, it causes some issues, and many host packages need different
dependencies than their target variants.

Now that host dependencies are explicitly set for all packages, we can
remove it.

Signed-off-by: Julien Floret <julien.floret@6wind.com>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>