Reg B 202.9(e) addresses withdrawals of approved applications:
(e) Withdrawal of approved application. When an applicant submits an application and the parties contemplate that the applicant will inquire about its status, if the creditor approves the application and the applicant has not inquired within 30 days after applying, the creditor may treat the application as withdrawn and need not comply with paragraph (a)(1) of this section.
When the application is just a plane withdrawal you should use the Adverse Action Notice. It is a filled out differently than a denial as it will be a notice of withdrawal.