Stop reporting ExternalIP field to clients

At best, it doesn't help compared to Moonlight's STUN logic.

At worst, it makes things worse by providing an incorrect WAN address that overrides STUN.

src/nvhttp.cpp

@@ -632,10 +632,6 @@ namespace nvhttp {
       tree.put("root.ServerCodecModeSupport", "3");
     }
 
-    if (!config::nvhttp.external_ip.empty()) {
-      tree.put("root.ExternalIP", config::nvhttp.external_ip);
-    }
-
     pt::ptree display_nodes;
     for (auto &resolution : config::nvhttp.resolutions) {
       auto pred = [](auto ch) { return ch == ' ' || ch == '\t' || ch == 'x'; };