Set Riot's enable_presence_by_hs_url to false if presence is disabled

roles/matrix-riot-web/templates/config.json.j2

@@ -14,6 +14,11 @@
 		"servers": {{ matrix_riot_web_roomdir_servers|to_json }}
 	},
 	"welcomeUserId": {{ matrix_riot_web_welcome_user_id|to_json }},
+	{% if matrix_synapse_use_presence|to_json %}
+	"enable_presence_by_hs_url": {
+		{{ matrix_riot_web_default_hs_url|to_json }}: false
+	},
+	{% endif %}
 	"embeddedPages": {
 		"homeUrl": {{ matrix_riot_web_embedded_pages_home_url|to_json }}
 	}