chore: remove dead makeNotImplementedPredicate helper

All 27 BUILTIN_PREDICATES now have real evaluators. The
makeNotImplementedPredicate factory and its IMH_FEATURE_NOT_YET_IMPLEMENTED
path were the last remaining NYI scaffolding — no caller existed for it.
IMH_FEATURE_NOT_YET_IMPLEMENTED diagnostic code kept in the taxonomy
as a future fallback, but no evaluator produces it.

packages/imhotep-solver/src/predicates.ts

@@ -988,32 +988,6 @@ export const withinPredicate: PredicateEvaluator = {
   },
 };
 
-// ---------------------------------------------------------------------------
-// Not-Yet-Implemented Predicates
-// ---------------------------------------------------------------------------
-
-function makeNotImplementedPredicate(name: string): PredicateEvaluator {
-  return {
-    descriptor: {
-      name,
-      arity: 2,
-      domains: ['element', 'element'],
-      requiredFacts: ['subject.primaryBox', 'reference.primaryBox'],
-    },
-    evaluateTuple(_world, tuple) {
-      const subjectId = tuple[0];
-      const referenceId = tuple[1];
-      return makePredicateResult('false', {}, [subjectId, referenceId].filter((id): id is number => id !== undefined), [
-        {
-          code: 'IMH_FEATURE_NOT_YET_IMPLEMENTED',
-          severity: 'error',
-          message: `Predicate "${name}" is not yet implemented.`,
-        },
-      ]);
-    },
-  };
-}
-
 export const separatedFromPredicate: PredicateEvaluator = {
   descriptor: BUILTIN_PREDICATES[18]!,
   evaluateTuple(world, tuple, options) {