Simplify extracting arguments from test calls

[eerovaher]

Among other things erfa_generator translates ERFA C tests to Python tests, which requires extracting arguments from C function calls. On current main there is the _get_funcname_and_args() helper for that purpose, but extracting function names is not useful because whenever the helper is called both the C function name and the corresponding pyerfa function name are already known. The new _args_from_func_call() does not bother with function names and allows deduplicating more code than _get_funcname_and_args() ever did. The full difference between the erfa/tests/test_ufunc.py generated by current main this PR is

583c583
<     ri, di = erfa_ufunc.atciqn (rc, dc, pr, pd, px, rv, astrom, b)
---
>     ri, di = erfa_ufunc.atciqn(rc, dc, pr, pd, px, rv, astrom, b)
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<     rc, dc, j = erfa_ufunc.atoc13 ("R", ob1, ob2, utc1, utc2, dut1, elong, phi, hm, xp, yp, phpa, tc, rh, wl)
---
>     rc, dc, j = erfa_ufunc.atoc13("R", ob1, ob2, utc1, utc2, dut1, elong, phi, hm, xp, yp, phpa, tc, rh, wl)
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<     rc, dc, j = erfa_ufunc.atoc13 ("H", ob1, ob2, utc1, utc2, dut1, elong, phi, hm, xp, yp, phpa, tc, rh, wl)
---
>     rc, dc, j = erfa_ufunc.atoc13("H", ob1, ob2, utc1, utc2, dut1, elong, phi, hm, xp, yp, phpa, tc, rh, wl)
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<     rc, dc, j = erfa_ufunc.atoc13 ("A", ob1, ob2, utc1, utc2, dut1, elong, phi, hm, xp, yp, phpa, tc, rh, wl)
---
>     rc, dc, j = erfa_ufunc.atoc13("A", ob1, ob2, utc1, utc2, dut1, elong, phi, hm, xp, yp, phpa, tc, rh, wl)
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<     ri, di, j = erfa_ufunc.atoi13 ("R", ob1, ob2, utc1, utc2, dut1, elong, phi, hm, xp, yp, phpa, tc, rh, wl)
---
>     ri, di, j = erfa_ufunc.atoi13("R", ob1, ob2, utc1, utc2, dut1, elong, phi, hm, xp, yp, phpa, tc, rh, wl)
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<     ri, di, j = erfa_ufunc.atoi13 ("H", ob1, ob2, utc1, utc2, dut1, elong, phi, hm, xp, yp, phpa, tc, rh, wl)
---
>     ri, di, j = erfa_ufunc.atoi13("H", ob1, ob2, utc1, utc2, dut1, elong, phi, hm, xp, yp, phpa, tc, rh, wl)
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<     ri, di, j = erfa_ufunc.atoi13 ("A", ob1, ob2, utc1, utc2, dut1, elong, phi, hm, xp, yp, phpa, tc, rh, wl)
---
>     ri, di, j = erfa_ufunc.atoi13("A", ob1, ob2, utc1, utc2, dut1, elong, phi, hm, xp, yp, phpa, tc, rh, wl)
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<     dr, dd = erfa_ufunc.g2icrs (dl, db)
---
>     dr, dd = erfa_ufunc.g2icrs(dl, db)
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<     dl, db = erfa_ufunc.icrs2g (dr, dd)
---
>     dl, db = erfa_ufunc.icrs2g(dr, dd)

In all cases the removal of whitespace is an improvement.