Remove unused dependencies

[tirz]

Hi o/

This PR remove unused dependencies for the irc crate (none was unused for irc-proto) and bump the dev-dependencies.

Note that they are still some libraries which need to be updated:

• bytes 0.5 => 0.6 (for irc-proto)
• tokio 0.2 => 0.3 (for irc and irc-proto)
• tokio-util 0.3 => 0.4 (for irc and irc-proto)
• tokio-rustls 0.14 => 0.20 (for irc)

But I wasn't brave enough... I never used tokio 0.3 and I am not even confident with the 0.2 version. Is it maybe better if some else can have a look first.

[tirz]

Hum... The example build-bot failed with Error: NoUsableNick :/ We can simply rename the bot but since he is not anymore on irc.pdgn.co but on chat.freenode.net, is this code still in use?

[tirz]

https://github.com/aatxe/irc/pull/220 is better.