Fix redundant checks around routerset_contains_XYZ()
The routerset_contains_foo() functions currently accept "NULL" in place of a routerset argument, with "NULL" denoting an empty routerset. (IOW, routerset_contains_node(NULL, node) always returns false.)
But our code acts like we don't know this: in lots of places, we say stuff like
if (set && routerset_contains_node(set, node)) {
}
which is redundant and silly. We can remove the "set &&" with no ill effect.
Note that this shouldn't be confused with
if (!set || routerset_contains_node(set, node)) {
}
which is how we say, "in this case, NULL means 'all nodes are included.'"
I'm tagging this as a ticket for 0.2.3.x. We should only do this once 0.2.2 has settled down a little more though, since the merges are likely to be conflicty given the router->node transition.