Remove CoreData and CoreDataProvider and use draftStore instead

Summary: This differential removes CoreData and CoredataProvider since they are not necesary. Drafts are now handled via redux

Test Plan: Open the app, write several drafts then kill the app. open app again and make sure drafts look like they were written before app was killed.

Reviewers: atul, tomek

Reviewed By: atul, tomek

Subscribers: ashoat, abosh

Differential Revision: https://phab.comm.dev/D5650