remove unused link target

Author: RalfJung

src/behavior-considered-undefined.md

@@ -126,7 +126,6 @@ must never exceed `isize::MAX`.
 [Rustonomicon]: ../nomicon/index.html
 [`NonNull<T>`]: ../core/ptr/struct.NonNull.html
 [`NonZero*`]: ../core/num/index.html
-[dereference expression]: expressions/operator-expr.md#the-dereference-operator
 [place expression context]: expressions.md#place-expressions-and-value-expressions
 [rules]: inline-assembly.md#rules-for-inline-assembly
 [points to]: #pointed-to-bytes