fix: remove oaep decrypt key size limit (#418) (#441)

As per #418, let me know if this is the preferred way or if you'd rather
remove the limit some other way

Co-authored-by: Gabriele Musco <gabmus@disroot.org>

src/oaep.rs

@@ -240,8 +240,6 @@ fn decrypt<R: CryptoRngCore + ?Sized>(
     mgf_digest: &mut dyn DynDigest,
     label: Option<String>,
 ) -> Result<Vec<u8>> {
-    key::check_public(priv_key)?;
-
     if ciphertext.len() != priv_key.size() {
         return Err(Error::Decryption);
     }