remove requirements on _pairing_ and `ark-poly-commit` (dragoon/komodo!54)

## changelog
- remove `ark-poly-commit` from the dependencies
- remove the old `setup.rs`
- add temporary `foo.rs` which define (some details are ommited for brevity)
  - `struct Powers<F, G>` 
  - `struct Commitment<F, G>`
  - `fn build_powers<F, G>(...) -> Powers<F, G>`
  - `fn commit<F, G, P>(powers: &Powers<F, G>, polynomial: &P) -> Commitment<F, G>`
  - tests
- `foo.rs` is then renamed to `setup.rs`
- two new `KomodoError` variants have been created to replace `ark_poly_commit::Error`
  - `DegreeIsZero`
  - `TooFewPowersInTrustedSetup(usize, usize)`
- finally, all the past mentions to `E: Pairing` and `setup::random` have been replaced with `F, G` and `setup::build_powers` respectively