build: switch to C++17
Change-Id: Ie68020a04b7e20b74778b6d0370544ded55c5e26
diff --git a/core/common.hpp b/core/common.hpp
index 01f794c..a5f47d9 100644
--- a/core/common.hpp
+++ b/core/common.hpp
@@ -50,11 +50,10 @@
#include <limits>
#include <map>
#include <memory>
+#include <optional>
#include <set>
#include <stdexcept>
#include <string>
-#include <unordered_map>
-#include <unordered_set>
#include <utility>
#include <vector>
@@ -66,7 +65,6 @@
#include <ndn-cxx/net/face-uri.hpp>
#include <ndn-cxx/util/backports.hpp>
#include <ndn-cxx/util/exception.hpp>
-#include <ndn-cxx/util/optional.hpp>
#include <ndn-cxx/util/scheduler.hpp>
#include <ndn-cxx/util/signal.hpp>
#include <ndn-cxx/util/span.hpp>
@@ -96,8 +94,6 @@
using namespace std::string_literals;
-using ndn::optional;
-using ndn::nullopt;
using ndn::span;
using ndn::to_string;