[native] Return inputState.sendMultimediaMessage Promise directly in ChatCameraModal

Summary:
The API of CameraModal doesn't care what the function returns, so we might as well return the Promise directly, as an alternative to prefixing with void.

Depends on D10171

Test Plan: Flow

Reviewers: atul, michal

Reviewed By: michal

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D10173