Update the `set_key_and_party_polynomials` function

[djordon]

Feature - Update the set_key_and_party_polynomials function

1. Description

Both the FROST and FIRE coordinators implement a function called set_key_and_party_polynomials that takes an aggregate key and the party polynomials and sets some struct fields from the input. These functions both take an aggregate key, but don't need to, since the function computes the aggregate key from the given polynomial commitments. Might was well simplify the function and remove the unnecessary input.

Also, the function needs a HashMap of the polynomials but takes a Vec. Better to change that to take what is needed.