[clang] [libunwind] [llvm] Replace documentation mentions of IRC with Discord (PR #114276)

[Erich Keane via llvm-commits]

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@@ -377,7 +377,6 @@ Guidance for office hours hosts
 
     * the `#office-hours Discord channel
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erichkeane wrote:

Weird to have a list of 1.

https://github.com/llvm/llvm-project/pull/114276