pkg-infra: remove self-dependency from host packages

When HOST_XXX_DEPENDENCIES are derived automatically from
XXX_DEPENDENCIES, a self-dependency is created if host-xxx is a dependency
of xxx.  This was the case for miniperl.

Filter out the self-dependency.

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>