EDIT

Synonym relationships are not necessarily needed as a synonym always belongs to 1 explicit taxon. They are only needed for pro parte synonyms, a concept not correct as pro parte indicates concept relationships.

As reusing of synonyms for this incorrect purpose was never asked by users we may remove it.

Open question is if synonym sec and synonym relationship citation are both needed. Probably not with syn sec being the reference saying that the synonym (name) is a synonym of the given concept. The synonym itself does not have a real secundum as it is not a concept, only a name usage. Synonyms mentionied in the same reference as the accepted taxon secundum will get the same syn sec.

This is according to the fact that we use "syn. sec." already instead of sec. for synonyms in dataportal/cache strategy.

We need to check if any reused synonyms exist and if any syn rel citations exist, which may get lost when removing the SynonymRelationship class.

see also #5523