Remove stale footnote

Footnote about function 'fun' is not in source code.

src/types/literals.md

@@ -30,14 +30,11 @@ fn main() {
 There are some concepts used in the previous code that haven't been explained
 yet, here's a brief explanation for the impatient readers:
 
-* `fun(&foo)` is used to pass an argument to a function *by reference*, rather
-  than by value (`fun(foo)`). For more details see [borrowing][borrow].
 * `std::mem::size_of_val` is a function, but called with its *full path*. Code
   can be split in logical units called *modules*. In this case, the
   `size_of_val` function is defined in the `mem` module, and the `mem` module
   is defined in the `std` *crate*. For more details, see
   [modules][mod] and [crates][crate].
 
-[borrow]: ../scope/borrow.md
 [mod]: ../mod.md
 [crate]: ../crates.md