[Telemetry] Move TestStreamOutput to unittest_util.

tools/telemetry/telemetry/results/base_test_results_unittest.py

Index: tools/telemetry/telemetry/results/base_test_results_unittest.py
diff --git a/tools/telemetry/telemetry/results/base_test_results_unittest.py b/tools/telemetry/telemetry/results/base_test_results_unittest.py
index 59295587027f4ab94a19eb5643da65e9b5db108d..84e04383cc0c250f2970a725a45d1e206986125a 100644
--- a/tools/telemetry/telemetry/results/base_test_results_unittest.py
+++ b/tools/telemetry/telemetry/results/base_test_results_unittest.py
@@ -7,19 +7,6 @@ import unittest
 from telemetry.core import exceptions
 
 
-class TestOutputStream(object):
-
-  def __init__(self):
-    self.output_data = []
-
-  def write(self, data):
-    assert isinstance(data, str)
-    self.output_data.append(data)
-
-  def flush(self):
-    pass
-
-
 class BaseTestResultsUnittest(unittest.TestCase):
 
   def CreateException(self):