Cleanup track files in test_x2sys_cross_input_two_filenames

[weiji14]

Description of proposed changes

The track_0.xyz and track_1.xyz input test files were not removed after test_x2sys_cross_input_two_filenames. Addresses #546 (comment).

Fixes #

Reminders

• Run make format and make check to make sure the code follows the style guide.
• Add tests for new features or tests that would have caught the bug that you're fixing.
• Add new public functions/methods/classes to doc/api/index.rst.
• Write detailed docstrings for all functions/methods.
• If adding new functionality, add an example to docstrings or tutorials.