Remove Poseidon, Poseidon2 (#1674)

### What

Remove Poseidon, Poseidon2 code from the sdk.

### Why

To prepare for migrating this into a separate repo, for independent
review/audit/release cadence from the regular sdk.

Author: jayz22

soroban-sdk/src/crypto.rs

@@ -8,14 +8,8 @@ use crate::{
 
 pub mod bls12_381;
 pub mod bn254;
-pub(crate) mod poseidon2_params;
-pub mod poseidon2_sponge;
-pub(crate) mod poseidon_params;
-pub mod poseidon_sponge;
 pub(crate) mod utils;
 pub use bn254::Fr as BnScalar;
-pub use poseidon2_sponge::{Poseidon2Config, Poseidon2Sponge};
-pub use poseidon_sponge::{PoseidonConfig, PoseidonSponge};
 
 /// A `BytesN<N>` generated by a cryptographic hash function.
 ///
@@ -198,47 +192,6 @@ impl Crypto {
     pub fn bn254(&self) -> bn254::Bn254 {
         bn254::Bn254::new(self.env())
     }
-
-    /// Computes a Poseidon hash matching circom's
-    /// [implementation](https://github.com/iden3/circomlib/blob/35e54ea21da3e8762557234298dbb553c175ea8d/circuits/poseidon.circom)
-    /// for input lengths up to 5 (`t ≤ 6`).
-    ///
-    /// Internally it picks the state size `t` to match the input length, i.e.
-    /// `t = N + 1` (rate = N, capacity = 1). For example, hashing 2 elements
-    /// uses t=3.
-    ///
-    /// Note: use [`poseidon_sponge::hash`] with a pre-constructed
-    /// [`PoseidonConfig`] directly if:
-    /// - You want to repeatedly hash with the same input size. Pre-constructing
-    ///   the config saves the cost of re-initialization.
-    /// - You want to hash larger input sizes. The sponge will repeatedly
-    ///   permute and absorb until the entire input is consumed. This is a valid
-    ///   (and secure) sponge operation, even though it may not match circom's
-    ///   output, which always picks a larger state size (N+1) to hash inputs in
-    ///   one shot (up to t=17). If you need parameter support for larger `t`,
-    ///   please file an issue.
-    pub fn poseidon_hash(&self, field_type: Symbol, inputs: &Vec<U256>) -> U256 {
-        let config = PoseidonConfig::new(&self.env, field_type, inputs.len() as u32);
-        poseidon_sponge::hash(&self.env, inputs, config)
-    }
-
-    /// Computes a Poseidon2 hash matching noir's
-    /// [implementation](https://github.com/noir-lang/noir/blob/abfee1f54b20984172ba23482f4af160395cfba5/noir_stdlib/src/hash/poseidon2.nr).
-    ///
-    /// Internally it always initializes the state with `t = 4`, regardless of
-    /// input length. It alternates between absorbing and permuting until all
-    /// input elements are consumed.
-    ///
-    /// Note: use [`poseidon2_sponge::hash`] with a pre-constructed
-    /// [`Poseidon2Config`] directly if:
-    /// - You need to hash multiple times. Pre-constructing the config saves the
-    ///   cost of re-initialization.
-    /// - You want to use a different state size (`t ≤ 4`).
-    pub fn poseidon2_hash(&self, field_type: Symbol, inputs: &Vec<U256>) -> U256 {
-        const INTERNAL_RATE: u32 = 3;
-        let config = Poseidon2Config::new(&self.env, field_type, INTERNAL_RATE);
-        poseidon2_sponge::hash(&self.env, inputs, config)
-    }
 }
 
 /// # ⚠️ Hazardous Materials