Cleanup track files in test_x2sys_cross_input_two_filenames (#552)

* Cleanup track files in test_x2sys_cross_input_two_filenames

* Fix pylint expression-not-assigned error

Author: weiji14

pygmt/tests/test_x2sys_cross.py

@@ -121,6 +121,7 @@ def test_x2sys_cross_input_two_filenames(mock_x2sys_home):
         columns = list(output.columns)
         assert columns[:6] == ["x", "y", "i_1", "i_2", "dist_1", "dist_2"]
         assert columns[6:] == ["head_1", "head_2", "vel_1", "vel_2", "z_X", "z_M"]
+        _ = [os.remove(f"track_{i}.xyz") for i in range(2)]  # cleanup track files
 
     return output