[iOS] Remove a stale TODO in `State.ts` and the unused constants export (#4457)

## Description

Removes two leftovers that reference each other:

- The `TODO use State from RNModule` comment in `src/State.ts`, added in
the TS rewrite (#1327). The idea was to source the `State` object from
the native module's exported constants instead of duplicating the values
in JS. That's no longer viable: the TurboModule spec has no
`getConstants`, web and Jest have no native module to ask, and `as
const` literal types have to exist at compile time anyway.

- The `constantsToExport` method in `RNGestureHandlerModule.mm` (the
`State` and `Direction` dictionaries, exported since 2017) together with
the now-unused `RNGestureHandlerDirection.h` import. Nothing on the JS
side reads these - without `getConstants` in the spec they are
unreachable on the new architecture.

`requiresMainQueueSetup` stays, as module initialization inserts into
the static `_managers` map that component views read on the main thread.

No behavior change.

## Test plan

- Built and ran `basic-example` on the iOS simulator; the app renders
and a tap on the `VirtualGestureDetector` text logs `Tapped on first
part!`.
- Verified nothing references the exported constants: no `getConstants`
in `NativeRNGestureHandlerModule.ts`, no `Module.State` /
`Module.Direction` reads in `src/`.