It's the end of an era. The IRC channel was previously where the
community gathered to discuss technical topics but is now a ghost town
where the primary activity is moderators (me) kickbanning the same
individual dozens of times a day for CoC violations and the secondary
activity is telling the occasional person to come to Discord for help.
The number of people engaging on IRC for the community's intended
purposes seems to be roughly one person a month.

So this removes all remaining mentions of IRC from our documentation so
that it no longer appears to be an "official" channel for communicating
with the community. It also removes IRC handles from the various
maintainers lists, since those would stand out as confusing
anachronisms.

The IRC channel topic already recommends people come to the Discord
server. There is no way to "shut down" an IRC channel such that it no
longer exists, so the channel will continue to exist on OFTC, but will
be unmoderated.

(This was previously discussed in https://discourse.llvm.org/c/llvm/5
but some mentions persisted.)

The list of Code of Conduct committee member names was out of date. This
updates it, and orders them alphabetically by last name.

This does not touch code owners or credits files that list IRC handles,
that can be done separately if we want to make that change.

See
https://discourse.llvm.org/t/rfc-remove-irc-as-a-recommended-communication-channel/82808/3
for the RFC.

Link restored from the original policy outlined here
https://discourse.llvm.org/t/code-of-conduct-changes-related-to-llvm-project-policy-changes/64197

This seemed like relevant information to include in the code of conduct.

Reviewed By: kristof.beyls

Differential Revision: https://reviews.llvm.org/D156456