[sledge] Improve using extended open
[sledge] Improve using extended open

Summary:
OCaml 4.08 supports `open` of arbitrary module expressions. This
enables some code simplifications.

Reviewed By: ngorogiannis

Differential Revision: D18736381

fbshipit-source-id: c729dcfbd

jvillard/infer,jvillard/infer,facebook/infer,facebook/infer,jvillard/infer,jvillard/infer,facebook/infer,facebook/infer,jvillard/infer,jvillard/infer,facebook/infer,facebook/infer,facebook/infer,jvillard/infer