[Buildbot] #3517: remove GitHubStatus from documentation

[Buildbot trac]

#3517: remove GitHubStatus from documentation
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Reporter:  rutsky     |      Owner:
    Type:  undecided  |     Status:  new
Priority:  major      |  Milestone:  0.9.0
 Version:  master     |   Keywords:
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 Looks like `GitHubStatus` was replaced with `GithubStatusPush`.

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Ticket URL: <http://trac.buildbot.net/ticket/3517>
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Buildbot: build/test automation