Function prune_sized_predicates 

fn prune_sized_predicates<'tcx>(
    tcx: TyCtxt<'tcx>,
    generic_predicates: &mut Predicates<'tcx>,
)

Given a GenericPredicates, prune every occurence of a sized-related clause. Prunes bounds of the shape T: MetaSized, T: Sized or T: PointeeSized.