chore: remove title from doc file

The title is rendered by astro no need to add it I didn't notice and
left some of those here and there. We should be good

Author: gianarb

docs/activity.md

@@ -4,8 +4,6 @@ sidebar:
   order: 3
 ---
 
-# Activity
-
 The `datumctl activity` command is available for interacting with the [activity
 service] we've made available to Datum Cloud consumers. The activity service
 allows users to query for audit logs that are collected for all interactions

docs/developer/releases.md

@@ -1,7 +1,6 @@
 ---
 title: "Releases"
 ---
-# Releases
 
 This guide explains how to cut a `datumctl` release locally with GoReleaser and
 how the GitHub Actions workflow publishes the official artifacts.