Clean up obsolete TODOs (#1734)

Squashed commit of the following:

commit f99373cbae
Author: Age Manning <Age@AgeManning.com>
Date:   Mon Oct 5 18:44:09 2020 +1100

    Clean up obsolute TODOs

beacon_node/eth2_libp2p/src/discovery/enr.rs

@@ -129,7 +129,6 @@ pub fn create_enr_builder_from_config<T: EnrKey>(config: &NetworkConfig) -> EnrB
         builder.udp(udp_port);
     }
     // we always give it our listening tcp port
-    // TODO: Add uPnP support to map udp and tcp ports
     let tcp_port = config.enr_tcp_port.unwrap_or_else(|| config.libp2p_port);
     builder.tcp(tcp_port).tcp(config.libp2p_port);
     builder