Do not include type_traits.hpp directly in the object index

json.hpp, which object_index.hpp already includes, provides it; included
directly, the json_view amalgamation (which only treats nlohmann/json.hpp
as external) copied the json internals into json_view.hpp a second time,
so the fuzzers, which include both single headers, failed with
redefinitions (make_void, integer_sequence, priority_tag, ...).

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

include/nlohmann/detail/view/object_index.hpp

@@ -13,7 +13,6 @@
 #include <cstring> // memcmp
 
 #include <nlohmann/json.hpp>
-#include <nlohmann/detail/meta/type_traits.hpp>
 #include <nlohmann/detail/view/document_data.hpp>
 #include <nlohmann/detail/view/macro_scope.hpp>
 #include <nlohmann/detail/view/node.hpp>