docs: Fix the section headings from the AI policy

Need to reduce the section heading by 1 to be consistent inside the
"Policies" heading.

Remove the nested "Policy" heading, because it doesn't add much and
looks awkward when included in `contributing.md`.

AI_POLICY.md

@@ -5,8 +5,6 @@ contributions as long as you review and edit what it produces to follow the
 project guidelines. However, please do not use AI and agents to communicate with
 the community, including Discord, issues, and pull requests.
 
-## Policy
-
 1. **You are the author.** AI is a tool you may use while creating a
    contribution, but you are the author.
 

docs/contributing.md

@@ -19,7 +19,7 @@ again. In other words, the Google CLA is not scoped to a specific project. If
 you sign the Google CLA, it applies to other Google open-source projects as
 well (including future projects).
 
-{% include-markdown '../AI_POLICY.md' heading-offset=1 %}
+{% include-markdown '../AI_POLICY.md' heading-offset=2 %}
 
 ### Commit guidelines