fs/archive: remove dead code

the std::hash bug is fixed in gcc 6.1, and we are now targeting 7.0 , so the workaround is no longer needed

src/core/hle/service/fs/archive.cpp

@@ -39,23 +39,6 @@
 #include "core/hle/service/service.h"
 #include "core/memory.h"
 
-// Specializes std::hash for ArchiveIdCode, so that we can use it in std::unordered_map.
-// Workaroung for libstdc++ bug: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60970
-namespace std {
-template <>
-struct hash<Service::FS::ArchiveIdCode> {
-    typedef Service::FS::ArchiveIdCode argument_type;
-    typedef std::size_t result_type;
-
-    result_type operator()(const argument_type& id_code) const {
-        typedef std::underlying_type<argument_type>::type Type;
-        return std::hash<Type>()(static_cast<Type>(id_code));
-    }
-};
-} // namespace std
-
-static constexpr Kernel::Handle INVALID_HANDLE{};
-
 namespace Service {
 namespace FS {