Fix Pi-hole deployment: remove undefined 'update gravity' handler notify

The 'Add aggressive blocklists' task notified a handler that didn't exist
in main.yml, causing deployment failure. Removed the notify since the
gravity update is already handled by the subsequent task.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

phantom/playbooks/dns/tasks/configure.yml

@@ -44,7 +44,6 @@
         - "https://raw.githubusercontent.com/StevenBlack/hosts/master/hosts"
         - "https://raw.githubusercontent.com/hagezi/dns-blocklists/main/adblock/pro.txt"
       when: pihole_blocklist == "aggressive"
-      notify: update gravity
 
     - name: Update gravity after blocklist changes
       command: pihole -g