Use dummy diffstat in tests and remove older diffstat workaround.
This makes test-notify pass on systems without diffstat installed
or where the diffstat version yields a different output.
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<title>Mercurial repository not found</title>
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<h2>Mercurial repository not found</h2>
The specified repository "#repo|escape#" is unknown, sorry.
Please go back to the main repository list page.
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