Remove doc link to private item.

Author: m-ou-se

library/core/src/fmt/mod.rs

@@ -428,10 +428,8 @@ impl<'a> Arguments<'a> {
     /// An `UnsafeArg` is required because the following invariants must be held
     /// in order for this function to be safe:
     /// 1. The `pieces` slice must be at least as long as `fmt`.
-    /// 2. Every [`rt::Placeholder::position`] value within `fmt` must be a
-    ///    valid index of `args`.
-    /// 3. Every [`rt::Count::Param`] within `fmt` must contain a valid index of
-    ///    `args`.
+    /// 2. Every `rt::Placeholder::position` value within `fmt` must be a valid index of `args`.
+    /// 3. Every `rt::Count::Param` within `fmt` must contain a valid index of `args`.
     #[doc(hidden)]
     #[inline]
     #[unstable(feature = "fmt_internals", reason = "internal to format_args!", issue = "none")]