[sledge] Update stale comment
[sledge] Update stale comment

Summary:
This has been out of date since arithmetic was changed from a purely
uninterpreted treatment to having a solver.

Reviewed By: jvillard

Differential Revision: D16985159

fbshipit-source-id: 39e42069c

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