doc: remove IRC node-dev link from README

The IRC link is mentioned in CONTRIBUTING.md which is linked immediately
above. We should encourage people to read that doc before hoping on the
IRC channel.

PR-URL: #17106
Ref: #16533 (comment)
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>

README.md

@@ -586,7 +586,6 @@ Information on the current Node.js Working Groups can be found in the
 ### Contributing to Node.js
 
 * [Contributing to the project][]
-* IRC (node core development): [#node-dev on chat.freenode.net][]
 
 [npm]: https://www.npmjs.com
 [Code of Conduct]: https://github.com/nodejs/TSC/blob/master/CODE_OF_CONDUCT.md
@@ -595,4 +594,3 @@ Information on the current Node.js Working Groups can be found in the
 [Node.js Website]: https://nodejs.org/en/
 [Questions tagged 'node.js' on StackOverflow]: https://stackoverflow.com/questions/tagged/node.js
 [#node.js channel on chat.freenode.net]: https://webchat.freenode.net?channels=node.js&uio=d4
-[#node-dev on chat.freenode.net]: https://webchat.freenode.net?channels=node-dev&uio=d4