Downgrade to Starscream `3.1.0`.#2

Open

MaximAlien wants to merge 3 commits intodevelopfrom

mm/downgrade-starscream

Commits on Aug 19, 2021

Update podspec to the new `2.4.0-zksync` version.
MaximAlien
committed

Commits on Aug 25, 2021

Remove submodule reference. (#1)
MaximAlien
authored

Commits on Sep 27, 2021

Downgrade to Starscream `3.1.0` to prevent library versions mismatch issues.
MaximAlien
committed