Remove #llvm buildbot as it doesn't scale to the size of the project anymore

Broadcasting all breakage to all IRC users isn't effective - more
buildbots, more failure modes, means that there's almost always some
noise & a single breakage can result in many redundant mails from
distinct buildbots, making the channel difficult to use.

Differential Revision: https://reviews.llvm.org/D87100
1 file changed