core: slim down `common.hpp`

Change-Id: I875c35147edd2261fbaa24e809c170d5cd9b94d3
diff --git a/tests/daemon/fw/topology-tester.hpp b/tests/daemon/fw/topology-tester.hpp
index e82705c..5264306 100644
--- a/tests/daemon/fw/topology-tester.hpp
+++ b/tests/daemon/fw/topology-tester.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2023,  Regents of the University of California,
+ * Copyright (c) 2014-2024,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University,
@@ -38,6 +38,8 @@
 
 #include <ndn-cxx/face.hpp>
 
+#include <unordered_map>
+
 namespace nfd::tests {
 
 /** \brief Identifies a node (forwarder) in the topology.