remove "unknown" parameters in get_latencies api call to latency server

web/app/controllers/api_users_controller.rb

@@ -949,8 +949,8 @@ class ApiUsersController < ApiController
       req.body = {
         my_user_id: current_user.id,
         my_public_ip: request.remote_ip,
-        my_device_id: 'unknown',
-        my_client_id: 'unknown',
+        my_device_id: nil,
+        my_client_id: nil,
         users: user_ids
       }.to_json