Delete specific BARTOC entry

[DavidBRohrer]

With the following search (https://bartoc.org/vocabularies?search=vorpommern) two entries of the same vocabulary are found. https://bartoc.org/en/node/1986 is the correct one and should be left.
https://bartoc.org/en/node/20398 is one entry too much and should be deleted.

Problem: at the moment, when deleting an entry, adding new entries works no more. This should be fixed before.

Further entries to delete;

• https://bartoc.org/en/node/18706 (https://bartoc.org/en/node/20303 is the right one)
• https://bartoc.org/en/node/20329 (https://bartoc.org/en/node/20000 is the right one)

[nichtich]

Deleting vocabularies breaks creation of new vocabularies. Requires gbv/jskos-server#161.

[DavidBRohrer]

see also #155

[stefandesu]

I adjusted the code for minting a new URI with the new feature in gbv/jskos-server#161. Deleting entries should now be possible without causing issues.

Note that when deleting the very latest record (i.e. currently highest ID), its URI will be reused for the next created record. Is that an issue @nichtich? If yes, we would need to save a counter somewhere...