[native] Set ITSAppUsesNonExemptEncryption to NO for iOS builds

Summary: See here... unblocks Testflight builds by circumventing some App Store Connect bug.

Test Plan: Upload a new Testflight build

Reviewers: atul, palys-swm

Reviewed By: atul

Subscribers: KatPo, zrebcu411, Adrian, subnub, karol-bisztyga

Differential Revision: https://phabricator.ashoat.com/D807