Remove abbData / aco-abbreviations.json

[pdaengeli]

Instead of abbData / aco-abbreviations.json the same information is available in aco-meta-docs.json (directly derived from the input files):

    "Abkürzungsverzeichnis": {                                                                                                                                  
      "text": "<article lang='de-DE'>
                   <h1 class='h1'>Abkürzungsverzeichnis</h1> 
                   <dl class='abbreviations'> 
                     <dt>ABAW.PPH</dt> 
                     <dd>Abhandlungen der Bayerischen Akademie der Wissenschaften, Philosophisch-philologische und historische Klasse</dd>
            etc etc

The name of the key is not nice, but it is lifted from the file name (with unicode normalisation). This is not perfectly deterministic, but if we get new exports it will be my responsibility to inspect the diffs and act as needed.

(I considered lower-casing the files but I didn't want to risk breaking anything when pushing to main.)

Current usage of abbData: https://github.com/search?q=repo%3ADHBern%2FACO%20abbdata&type=code