[sledge] Tighten test for uninterp terms in Context.solve_uninterp_eqs
[sledge] Tighten test for uninterp terms in Context.solve_uninterp_eqs

Summary:
Context.solve_uninterp_eqs uses `not Theory.is_interpreted` where
`Theory.is_noninterpreted` is more correct, since it operates on terms
that are class elements, which cannot be `Z _ | Q _ | Concat [||]`.

Reviewed By: jvillard

Differential Revision: D25883732

fbshipit-source-id: 5d060b338

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