{README,CONTRIBUTING}: drop obsolete communication channels

Drop mentions of coreos-dev mailing list and Freenode #coreos channel,
since they're not active anymore.

CONTRIBUTING.md

@@ -12,15 +12,6 @@ Origin (DCO). This document was created by the Linux Kernel community and is a
 simple statement that you, as a contributor, have the legal right to make the
 contribution. See the [DCO](DCO) file for details.
 
-# Email and Chat
-
-The project currently uses the general CoreOS email list and IRC channel:
-- Email: [coreos-dev](https://groups.google.com/forum/#!forum/coreos-dev)
-- IRC: #[coreos](irc://irc.freenode.org:6667/#coreos) IRC channel on freenode.org
-
-Please avoid emailing maintainers found in the MAINTAINERS file directly. They
-are very busy and read the mailing lists.
-
 ## Getting Started
 
 - Fork the repository on GitHub

README.md

@@ -51,8 +51,6 @@ flannel is also widely used outside of kubernetes. When deployed outside of kube
 
 ## Contact
 
-* Mailing list: coreos-dev
-* IRC: #coreos on freenode.org
 * Slack: #flannel on [Calico Users Slack](https://slack.projectcalico.org)
 * Planning/Roadmap: [milestones][milestones], [roadmap][roadmap]
 * Bugs: [issues][flannel-issues]