_guides/resources.md links to an unused irc channel

[dcermak]

The channel #letstest.js on Freenode as mentioned in:

chaijs.github.io/_guides/resources.md

Line 17 in 89f0377

directly on Twitter. Chai developers can also be found on Freenode IRC in #letstest.js.

does not appear to be used anymore. Should the reference be removed?