Remove invalid doc links.

Author: Amanieu

Diff for: compiler/rustc_codegen_cranelift/src/inline_asm.rs

@@ -1,4 +1,4 @@
-//! Codegen of [`asm!`] invocations.
+//! Codegen of `asm!` invocations.
 
 use crate::prelude::*;
 

Diff for: compiler/rustc_hir/src/def.rs

@@ -113,7 +113,7 @@ pub enum DefKind {
     Field,
     /// Lifetime parameter: the `'a` in `struct Foo<'a> { ... }`
     LifetimeParam,
-    /// A use of [`global_asm!`].
+    /// A use of `global_asm!`.
     GlobalAsm,
     Impl,
     Closure,