[native] remove unused types

Summary:
Introduced some types with the intention of simplifying our code but it proved too difficult. Removing them for now since they're unused.

Depends on D4950

Test Plan: cargo build

Reviewers: tomek, karol, atul

Reviewed By: atul

Subscribers: ashoat, abosh

Differential Revision: https://phab.comm.dev/D4951