doc(book/ffi): remove duplicate link reference `[libc]'

diff --git a/src/doc/book/ffi.md b/src/doc/book/ffi.md
index d949bf33b6eeaa458e9a4a051744d824602d3025..c3896e4e9c55737ad35d2b1d24046c34f54bcb61 100644 (file)
--- a/src/doc/book/ffi.md
+++ b/src/doc/book/ffi.md
@@ -517,8 +517,6 @@ The [`libc` crate on crates.io][libc] includes type aliases and function
 definitions for the C standard library in the `libc` module, and Rust links
 against `libc` and `libm` by default.
 
-[libc]: https://crates.io/crates/libc
-
 # The "nullable pointer optimization"
 
 Certain types are defined to not be `null`. This includes references (`&T`,