Fix flaky durations test

Unfortunately due to fluctuations in runtime "test_something"
might still appear in the final message.

Example failure:

https://ci.appveyor.com/project/pytestbot/pytest/builds/19494829/job/8lx847u0c78m63wf

testing/acceptance_test.py

@@ -808,7 +808,6 @@ class TestDurations(object):
         result.stdout.fnmatch_lines_random(
             ["*durations*", "*call*test_3*", "*call*test_2*"]
         )
-        assert "test_something" not in result.stdout.str()
         result.stdout.fnmatch_lines(
             ["(0.00 durations hidden.  Use -vv to show these durations.)"]
         )