docs: drop the Cloud release line from v26.38.2

v26.38.2 is not being released to Materialize Cloud, so the section keeps
only its Self-Managed line. The compatibility table row is unaffected: it
records the Self-Managed operator release, which is still happening.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: bosconi

doc/user/content/releases/_index.md

@@ -20,7 +20,6 @@ both Cloud and Self-Managed. See [Release schedule](/releases/schedule) for deta
 {{</ note >}}
 
 ## v26.38.2
-*Released to Materialize Cloud: 2026-08-24* <br>
 *Released to Materialize Self-Managed: 2026-08-25* <br>
 
 ### Agent Skills {#v26.38.2-agent-skills}