Remove erroneous member declaration in farey_symbol

[user202729]

As you can see in the C++ header file, there is in fact no members named a, b, c, d. In fact it's an error in C++ to have a member function and member variable with the same name.

Newer versions of Cython gives hard-to-debug errors for this.

📝 Checklist

• The title is concise and informative.
• The description explains in detail what this PR is about.
• I have updated the documentation and checked the documentation preview.

⌛ Dependencies

[user202729]

2024-12-09T01:45:53.8299280Z   sage/libs/braiding.cpp: In function 'PyObject* __pyx_pf_4sage_4libs_8braiding_30cyclic_slidings(PyObject*, PyObject*)':
2024-12-09T01:45:53.8300433Z   sage/libs/braiding.cpp:8947:27: error: 'CyclicSlidings' is not a member of 'Braiding'
2024-12-09T01:45:53.8301384Z    8947 |   __pyx_v_rop = Braiding::CyclicSlidings(__pyx_t_5, __PYX_STD_MOVE_IF_SUPPORTED(__pyx_t_6));
2024-12-09T01:45:53.8302090Z         |                           ^~~~~~~~~~~~~~

Weird but… looks unrelated to the change…? I guess I'll just wait for these (unrelated) issues to be fixed in master.

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[github-actions]

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