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/examples/download_avatars.rs

@@ -1,5 +1,4 @@
 use futures::stream::StreamExt;
-use std::convert::TryFrom;
 use std::env::args;
 use std::fs::{create_dir_all, File};
 use std::io::{self, Write};