Adobe will not charge you after the trial period, which I think is only 7 days, not 30, If you want to subscribe to the CC or to buy Lightroom 6, it s up to you to act. If you do not subscribe or buy, you will not be able to use the Develop Module, other than that, there is nothing that has to be canceled. If you have no credit card entered, they have no card to charge against.
i have no credit card
Then you have nothing to worry about. They won't be sending you an invoice in the mail.