Update edition to 2021

- Remove TryFrom/Into and FromIterator imports
- Prevent impl_validator_using_provider macro in sasl crate from
  constructing trait object

Signed-off-by: Maxime “pep” Buquet <pep@bouah.net>

tokio-xmpp/src/client/auth.rs

@@ -4,7 +4,6 @@ use sasl::client::Mechanism;
 use sasl::common::scram::{Sha1, Sha256};
 use sasl::common::Credentials;
 use std::collections::HashSet;
-use std::convert::TryFrom;
 use std::str::FromStr;
 use tokio::io::{AsyncRead, AsyncWrite};
 use xmpp_parsers::sasl::{Auth, Challenge, Failure, Mechanism as XMPPMechanism, Response, Success};