Discard the description of status code 0

[eerovaher]

Many ERFA functions return a status code which is used by the Python wrappers to raise an error or emit a warning. The error or warning messages are taken from the ERFA C doc comments and stored in a module level dictionary. Status code 0 always means that there were no warnings or errors, so there is no message to display to the user and the descriptions do not have to be stored.

EDIT: The full difference between erfa/core.py generated on current main and in this PR is

334d333
<         0: "OK",
341d339
<         0: "OK",
346d343
<         0: "OK",
351d347
<         0: "OK",
356d351
<         0: "OK",
361d355
<         0: "OK",
366d359
<         0: "OK",
370d362
<         0: "OK",
377d368
<         0: "OK",
382d372
<         0: "OK",
393d382
<         0: "OK",
402d390
<         0: "OK",
406d393
<         0: "OK",
410d396
<         0: "OK",
415d400
<         0: "OK",
420d404
<         0: "OK",
425d408
<         0: "OK",
429d411
<         0: "OK",
434d415
<         0: "OK",
439d419
<         0: "OK",
445d424
<         0: "no warnings or errors",
452d430
<         0: "OK",
458d435
<         0: "no warnings or errors",
465d441
<         0: "no warnings",
473d448
<         0: "OK",
477d451
<         0: "OK",
483d456
<         0: "OK",
489d461
<         0: "OK",
495d466
<         0: "OK",
502d472
<         0: "OK",
507d476
<         0: "OK",
512d480
<         0: "OK",