ignore families for L2 guard independence

mike is concerned that we would get too much exposure to adversaries,
if we enforce that none of our L2 guards can be in the same family.

this change set now essentially finishes the feature that commit a77727cdc
was attempting to add, but strips the "_and_family" part of that plan.

src/feature/client/entrynodes.c

@@ -4139,10 +4139,11 @@ maintain_layer2_guards(void)
   /* First gather the exclusions based on our current L2 guards */
   smartlist_t *excluded = smartlist_new();
   SMARTLIST_FOREACH_BEGIN(layer2_guards, layer2_guard_t *, g) {
-    /* Exclude existing L2 guard + family so that we don't double-pick. */
+    /* Exclude existing L2 guard so that we don't double-pick it.
+     * But, it's ok if they come from the same family. */
     const node_t *existing = node_get_by_id(g->identity);
     if (existing)
-      nodelist_add_node_and_family(excluded, existing);
+      smartlist_add(excluded, (node_t *)existing);
   } SMARTLIST_FOREACH_END(g);
 
   /* Add required guards to the list */
@@ -4167,8 +4168,9 @@ maintain_layer2_guards(void)
     // Nickname can also be None here because it is looked up later
     control_event_guard("None", layer2_guard->identity,
                         "GOOD_L2");
-    /* Exclude this node and its family so that we don't double-pick. */
-    nodelist_add_node_and_family(excluded, choice);
+    /* Exclude this node so that we don't double-pick it. (Again, coming
+     * from the same family is ok here.) */
+    smartlist_add(excluded, (node_t *)choice);
   }
 
   /* Some cleanup */