Revert "Expand and fixup 00d87f8"

This reverts commit 52a516cfb7.

src/config.hpp

@@ -49,10 +49,7 @@
 #include "config_attribute_value.hpp"
 #include "exceptions.hpp"
 
-#ifdef HAVE_CXX17
-#include <string_view>
-using config_key_type = std::string_view;
-#elif BOOST_VERSION > 106100
+#if BOOST_VERSION > 106100
 #include <boost/utility/string_view.hpp>
 using config_key_type = boost::string_view;
 #else

src/serialization/string_view.hpp

@@ -27,8 +27,6 @@ that class. */
 /** Use the standard library string_view if building with C++17. */
 #ifdef HAVE_CXX17
 
-#include <string_view>
-
 namespace utils {
 using string_view = std::string_view;
 typedef std::basic_string_view<uint8_t, std::char_traits<uint8_t>> byte_string_view;