Remove extra/bad CV terms in some cases

[IgorRodchenkov]

CV checking/auto-fixing is currently performed as follows: if there are more than one values in a CV.term property, and there are UnificationXrefs (normally one), then we keep only one valid term per valid xref and remove other values, which (removing) is probably bad idea...

We saw examples where a CellularLocationVocabulary has one xref and several term values:
"Mitochondrial Intermembrane Space", "GO:0005758", "mitochondrial intermembrane space".