Do not clamp generated private key in X25519 (new format)

This was required by legacy ECDH over curve25519, but not for the new format.
Relevant spec: https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-10.html#name-curve25519legacy-ecdh-secre

src/crypto/public_key/elliptic/ecdh_x.js

@@ -27,8 +27,6 @@ export async function generate(algo) {
     case enums.publicKey.x25519: {
       // k stays in little-endian, unlike legacy ECDH over curve25519
       const k = getRandomBytes(32);
-      k[0] &= 248;
-      k[31] = (k[31] & 127) | 64;
       const { publicKey: A } = nacl.box.keyPair.fromSecretKey(k);
       return { A, k };
     }