doc: remove IRC from man page

Our community communication channels come and go, whether that's Freenode or Libera or Slack or whatever other community channels there were at some point, and I simply do not believe that folks regularly see this information at the end of the man page and benefit from it more than from going to our GitHub repository or website (both of which contain references to GitHub, discussions, issues, IRC, Slack, ...).

More importantly, if someone looks at the man page of an outdated version of the Node.js, this way they won't be directed at a potentially outdated or non-existing resource. (Assuming GitHub is here to stay.)