Remove compiler_builtins_lib documentation

Fixes rust-lang#67593

Author: kraai

src/doc/unstable-book/src/language-features/lang-items.md

@@ -188,11 +188,7 @@ pub extern fn rust_begin_panic(info: &PanicInfo) -> ! {
 
 In many cases, you may need to manually link to the `compiler_builtins` crate
 when building a `no_std` binary. You may observe this via linker error messages
-such as "```undefined reference to `__rust_probestack'```". Using this crate
-also requires enabling the library feature `compiler_builtins_lib`. You can read
-more about this [here][compiler-builtins-lib].
-
-[compiler-builtins-lib]: ../library-features/compiler-builtins-lib.md
+such as "```undefined reference to `__rust_probestack'```".
 
 ## More about the language items