Duplicate code getting parametricity classes

[ecranceMERCE]

There seems to be a duplicate implementation of a predicate that gets all parametricity classes (i.e., annotations on universes, variable or ground) present in a type.

https://github.com/coq-community/trocq/blob/95f083ad0b3bca87324437d835b5957b9bd6a6cd/elpi/param-class.elpi#L320-L351

https://github.com/coq-community/trocq/blob/95f083ad0b3bca87324437d835b5957b9bd6a6cd/elpi/annot.elpi#L97-L131

It would be nice to check whether there is an important difference between them, and document it, or drop one of them.