mathlib

059eba46 - fix(category/preadditive/single_obj): remove superfluous instance (#9155)

fix(category/preadditive/single_obj): remove superfluous instance (#9155) Per @fpvandoorn's [new linter](https://leanprover.zulipchat.com/#narrow/stream/113488-general/topic/type-class.20loops.20in.20category.20theory).