Remove illegal std::to_string definition and use ndn::to_string in its place

Change-Id: I81481fea3267bde669c45df182e0aea8ccd1a188
Refs: #3214
diff --git a/common.hpp b/common.hpp
index 25cc4a6..3e4f44f 100644
--- a/common.hpp
+++ b/common.hpp
@@ -101,6 +101,8 @@
 using std::ref;
 using std::cref;
 
+using ndn::to_string;
+
 using ndn::Interest;
 using ndn::Data;
 using ndn::Name;
@@ -121,16 +123,4 @@
 
 } // namespace nfd
 
-// Some platforms are missing std::to_string (issue #2743)
-#ifndef HAVE_STD_TO_STRING
-namespace std {
-template<typename V>
-inline std::string
-to_string(const V& v)
-{
-  return boost::lexical_cast<std::string>(v);
-}
-} // namespace std
-#endif // HAVE_STD_TO_STRING
-
 #endif // NFD_COMMON_HPP