Clean up old Cxx TM member generation (facebook#43710)

Summary:
Pull Request resolved: facebook#43710

As we had already cut a branch for RN 0.74
https://github.com/facebook/react-native/releases/tag/v0.74.0-rc.1

We can delete this code already

Changelog: [Internal]

Reviewed By: shwanton

Differential Revision: D55511382

fbshipit-source-id: 3ef15af338b5ad31b02e0a1eed7ac873566d9562