auto merge of rust-lang#16198 : cakebaker/rust/remove_unused_tuple_struct, r=steveklabnik

Author: bors

src/doc/guide.md

@@ -1060,7 +1060,6 @@ you create a new type that's a synonym for another one:
 
 ```
 struct Inches(int);
-struct Centimeters(int);
 
 let length = Inches(10);