fix(agent.lua): Only set queries by default if no endpoints are defined including snet.

Currently if you define a `snet_region` in the agent configuration, it will complain that only one of `snet_region`, `queries`, or `endpoints` may be set. We were only checking if `queries` and `endpoint` were defined before setting `queries` by default.

Since we are setting a default endpoint now in `queries`, this removes the warning and early exit about not having any of them defined.