[CryptoModule] remove decryptSequential API

Summary:
This is only our wrapper over olm - we don't need it anymore so removing it to cleanup the code and avoid confusing which method should be used. (Removing our wrapper, olm API remains unchanged),

Depends on D12749

Test Plan: Build native app

Reviewers: marcin, tomek

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D12913