Refactoring entity_resolution (infiniflow#2692)

### What problem does this PR solve?

### Type of change

- [x] Refactoring

graphrag/entity_resolution.py

@@ -94,11 +94,7 @@ def __call__(self, graph: nx.Graph, prompt_variables: dict[str, Any] | None = No
 
         candidate_resolution = {entity_type: [] for entity_type in entity_types}
         for k, v in node_clusters.items():
-            candidate_resolution_tmp = []
-            for a, b in itertools.permutations(v, 2):
-                if self.is_similarity(a, b) and (b, a) not in candidate_resolution_tmp:
-                    candidate_resolution_tmp.append((a, b))
-            candidate_resolution[k] = candidate_resolution_tmp
+            candidate_resolution[k] = [(a, b) for a, b in itertools.combinations(v, 2) if self.is_similarity(a, b)]
 
         gen_conf = {"temperature": 0.5}
         resolution_result = set()