specify salt and version in ctor when encrypting

specify salt and version in ctor when encrypting

Simplify the signature of Encrypt.next() by removing the salt and
version arguments: This will make the encryptor reuse the values
it already has which was either passed to or randomly generated
by the ctor. Currently there is no case where we’d need to change
the salt or version during encryption. When decrypting, the
values from the headers are used anyways so nothing changes over
there.