[de] ISBN are no longer parsed

[daxida]

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https://kaikki.org/dewiktionary/Deutsch/meaning/G/Ga/Garage.html
https://de.wiktionary.org/wiki/Garage#Deutsch

Here, it should have been after Zurich 2017.

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Edit: I remember that @xxyzz removed some fields here and indeed the isbn seems to be among them.

It still feels odd to have an empty space between commas, so I will leave the issue open at your discretion, but feel free to close it if you don't think it deserves your time.

[xxyzz]

The problem is the "#isbn" parser function used in the "Vorlage:Literatur" template is not implemented, it's unrelated to my previous commit.