Remove NativeMethods exports (Strict API) (#57032)

Summary:

Actions the existing/pending deprecations in the preceding diff.

In our Flow source / Strict TypeScript API, the `NativeMethods` type was already deprecated (differing from D107119545).

Changelog:
[General][Breaking] - **Strict TypeScript API**: Remove legacy `NativeMethods` and `NativeMethodsMixin` types

Differential Revision: D107129357

Author: huntie