[native] Remove HelloWorld expo module

Summary:
Removed the scaffolded hello world module. It was only needed when other modules were not yet moved into the umbrella module.

Depends on D7963

Test Plan: This was not used anywhere, just ensured that the app still builds.

Reviewers: ashoat, atul, marcin

Reviewed By: ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D7964