ndnsec: improve error reporting when loading a Certificate or SafeBag fails

Refs: #5164
Change-Id: I6f594a921bb063ad808f311d8ff978bf0f7d528d
diff --git a/tools/ndnsec/cert-dump.cpp b/tools/ndnsec/cert-dump.cpp
index 5a388d7..9f86f1c 100644
--- a/tools/ndnsec/cert-dump.cpp
+++ b/tools/ndnsec/cert-dump.cpp
@@ -22,8 +22,6 @@
 #include "ndnsec.hpp"
 #include "util.hpp"
 
-#include "ndn-cxx/util/io.hpp"
-
 #include <boost/asio/ip/tcp.hpp>
 #if BOOST_VERSION < 106700
 #include <boost/date_time/posix_time/posix_time_duration.hpp>
@@ -109,13 +107,7 @@
 
   security::Certificate certificate;
   if (isFileName) {
-    try {
-      certificate = loadCertificate(name);
-    }
-    catch (const CannotLoadCertificate&) {
-      std::cerr << "ERROR: Cannot load the certificate from `" << name << "`" << std::endl;
-      return 1;
-    }
+    certificate = loadFromFile<security::Certificate>(name);
   }
   else {
     KeyChain keyChain;