Don't implement lang items on testing
Don't implement lang items on testing

The `std` library is imported on testing. It already implements all lang items.

phil-opp/blog_os,phil-opp/blog_os,phil-opp/blogOS,phil-opp/blog_os,phil-opp/blogOS,rafalmiel/blog_os,phil-opp/blog_os,rafalmiel/blog_os