COMP: Remove diversity-statement cross-reference

Section-level cross-references across documents are not supported in
Myst.

Addresses:

```
/home/matt/src/ITK/Documentation/docs/contributing/code_of_conduct.md:358: WARNING: local id not found in doc 'contributing/motivation': 'diversity-statement' [myst.xref_missing]
```

Documentation/docs/contributing/code_of_conduct.md

@@ -357,7 +357,7 @@ Harassment will not be tolerated in any of its forms either. Specifically:
 
 Although the above list cannot be exhaustive, we will not tolerate
 discrimination based on any of the protected characteristics in our
-[Diversity Statement](motivation.md#diversity-statement).
+[Diversity Statement](motivation.md).
 
 The relative anonymity (if any) in the discussion forums is no shelter for
 unacceptable behavior.