[identity] delete otk data on logout

Summary:
introduce new db method to delete all one-time keys for a given userID + deviceID. call this method on logout

https://linear.app/comm/issue/ENG-7920/one-time-keys-are-not-deleted-during-logout-delete-rpcs

Test Plan: logged out on simulator and confirmed on staging that the OTKs for that device were deleted

Reviewers: bartek

Reviewed By: bartek

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D11755