Removed the whitebox attribute.

Signed-off-by: Maciej Kurc <mkurc@antmicro.com>

tests/net_attr/child/child.sim.v

diff --git a/tests/net_attr/child/child.sim.v b/tests/net_attr/child/child.sim.v
index ec0bbf0..e09db94 100644
--- a/tests/net_attr/child/child.sim.v
+++ b/tests/net_attr/child/child.sim.v
@@ -1,4 +1,3 @@
-(* whitebox *)
 module CHILD(
     input  wire I,
     output wire O