Slim down `ndncert-common.hpp`

Change-Id: Ifba0966d3787c5cbf770963b82cba054ee1fe791
diff --git a/src/redirection/redirection-email.cpp b/src/redirection/redirection-email.cpp
index c13ad91..17e03d5 100644
--- a/src/redirection/redirection-email.cpp
+++ b/src/redirection/redirection-email.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2017-2022, Regents of the University of California.
+ * Copyright (c) 2017-2024, Regents of the University of California.
  *
  * This file is part of ndncert, a certificate management system based on NDN.
  *
@@ -20,8 +20,6 @@
 
 #include "redirection-email.hpp"
 
-#include <boost/algorithm/string.hpp>
-
 namespace ndncert {
 
 NDNCERT_REGISTER_REDIRECTION_POLICY(RedirectionEmail, "email");