Delete transactional.adoc (grails#852)

this property now has no effect and is irrelevant. As discussed in community here https://grails.slack.com/archives/C07M0GTDE/p1676569458998149?thread_ts=1676569265.733909&cid=C07M0GTDE https://docs.grails.org/5.2.5/guide/pages/declarativeTransactions.html explains this further