(TK-52) Remove default endpoint requirement

This PR removes the default endpoint requirement from the webrouting service. If no route-id is specified when calling a service function, the operation will still try to use the route with id of `:default`. However, it is no longer a requirement that this key be present.

It didn't seem worth it to allow the user to specify a default web route in a way similar to how the user would specify a default server, since a web route is intended to have something added to it only once.
I think I might get rid of this var from the let and put the `and` block directly into the `cond`.  Took me a second to try to understand what the var name meant but I think it'd be pretty clear right above the exception.