Remove redundant imports

These became warnings in a recent nightly.

The TryFrom/TryInto imports were missed in
4089891f6c, but the rest are truly
redundant.

xmpp/examples/hello_bot.rs

@@ -4,7 +4,6 @@
 // License, v. 2.0. If a copy of the MPL was not distributed with this
 // file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
-use env_logger;
 use std::env::args;
 use std::str::FromStr;
 use tokio_xmpp::parsers::{message::MessageType, BareJid, Jid};