refactor(test): remove unnecessary extxyz alias test per reviewer feedback

Co-authored-by: njzjz <9496702+njzjz@users.noreply.github.com>

Author: Copilot

tests/test_xyz.py

@@ -44,37 +44,3 @@ def setUp(self):
         with tempfile.NamedTemporaryFile("r") as f_xyz:
             self.system_1.to("xyz", f_xyz.name)
             self.system_2 = dpdata.System(f_xyz.name, fmt="xyz")
-
-
-class TestExtXYZAlias(unittest.TestCase):
-    def test_extxyz_alias_equivalence(self):
-        """Test that extxyz alias produces same results as quip/gap/xyz."""
-        # Use existing test file that works with quip/gap/xyz format
-        test_file = "xyz/xyz_unittest.xyz"
-        
-        # Load with quip/gap/xyz format
-        ms1 = dpdata.MultiSystems.from_file(test_file, "quip/gap/xyz")
-        # Load with extxyz alias
-        ms2 = dpdata.MultiSystems.from_file(test_file, "extxyz")
-        
-        # Should have same number of systems
-        self.assertEqual(len(ms1.systems), len(ms2.systems))
-        
-        # System keys should match
-        self.assertEqual(list(ms1.systems.keys()), list(ms2.systems.keys()))
-        
-        # Compare first system
-        if ms1.systems:
-            key = list(ms1.systems.keys())[0]
-            sys1 = ms1.systems[key]
-            sys2 = ms2.systems[key]
-            
-            # Basic properties should match
-            self.assertEqual(len(sys1), len(sys2))
-            self.assertEqual(sys1["atom_names"], sys2["atom_names"])
-            np.testing.assert_array_equal(sys1["atom_types"], sys2["atom_types"])
-            np.testing.assert_array_almost_equal(sys1["coords"], sys2["coords"])
-            
-            # Check that both have energies (labeled system property)
-            if "energies" in sys1.data:
-                np.testing.assert_array_almost_equal(sys1["energies"], sys2["energies"])