Enable rescinding from AppDelegate on iOS

Summary: This differential removes codeVersion blockade that prevented us from rescinding notifications via AppDelegate callbacks.

Test Plan: Create rescinding environment for iOS - one web client A and two clients B (mobile and web). Send message from A to B and read it on web version of B. Check in XCode debugger that rescinding code in AppDelegate is executed.

Reviewers: palys-swm

Reviewed By: palys-swm

Subscribers: ashoat, Adrian, atul, yayabosh

Differential Revision: https://phab.comm.dev/D4226