Remove unused includes
Remove unused includes

Summary:
These are mostly vestigial from forking from Hack. The stdint case can be
removed because the OCaml runtime API already defines types like uint64_t. The
OCaml runtime actually includes a lot of nice definitions, since the runtime is
highly portable.

Reviewed By: gabelevi

Differential Revision: D19267095

fbshipit-source-id: 0afc8ce5fb031674e117557938f8f91b4f80cf48

facebook/flow,facebook/flow,samwgoldman/flow,samwgoldman/flow,samwgoldman/flow,facebook/flow,mroch/flow,mroch/flow,facebook/flow,mroch/flow,samwgoldman/flow,facebook/flow,samwgoldman/flow,mroch/flow,mroch/flow,mroch/flow,mroch/flow,samwgoldman/flow,facebook/flow,facebook/flow,samwgoldman/flow