Removed brute force warning. It is no longer necessary

Author: Joao Felipe Rocha

test/test_knn.py

@@ -402,18 +402,15 @@ def bandwidth(x):
 
 
 def test_knn_graph_sparse_no_pca():
-    with assert_warns_message(
-        UserWarning, "cannot use tree with sparse input: using brute force"
-    ):
-        build_graph(
-            sp.coo_matrix(data),
-            n_pca=None,  # n_pca,
-            decay=10,
-            knn=3,
-            thresh=1e-4,
-            random_state=42,
-            use_pygsp=True,
-        )
+    build_graph(
+        sp.coo_matrix(data),
+        n_pca=None,  # n_pca,
+        decay=10,
+        knn=3,
+        thresh=1e-4,
+        random_state=42,
+        use_pygsp=True,
+    )
 
 
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