Revert 7642 "Fix memcheck and dr memory after flakiness dashboar..."

Reason: Turns out this does not solve the problem as the buildbots
run into another error later on during collecting gtest output.
The problem is solved by excluding these bots from flakiness dashboard
data instead, in https://codereview.chromium.org/705913002/

> Fix memcheck and dr memory after flakiness dashboard deployment.
> 
> I deployed buildbot configuration for uploading data to the
> flakiness dashboard but I didn't predict our Dr Memory and
> Memcheck bots would fail due to the new flag passed to the test.
> Adding the --gtest_output flag to the script will avoid the build
> to fail as a workaround.
> 
> TBR=andrew@webrtc.org
> TESTED=Passing test run using:
> src/tools/valgrind-webrtc/webrtc_tests.sh --test audio_decoder_unittests --tool memcheck --target Release --build-dir src/out --gtest_output=xml:audio_decoder_unittests.xml
> 
> BUG=
> 
> Review URL: https://webrtc-codereview.appspot.com/28999004

TBR=kjellander@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/31969004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7643 4adac7df-926f-26a2-2b94-8c16560cd09d

tools/valgrind-webrtc/webrtc_tests.py

@@ -100,9 +100,6 @@ def main(_):
                     help='Argument for --gtest_repeat')
   parser.add_option("--gtest_shuffle", action="store_true", default=False,
                     help="Randomize tests' orders on every iteration.")
-  parser.add_option('', '--gtest_output',
-                    help=('Argument for --gtest_output (ignored but included '
-                          'for compatibility).'))
   parser.add_option('-v', '--verbose', action='store_true', default=False,
                     help='Verbose output - enable debug log messages')
   parser.add_option('', '--tool', dest='valgrind_tool', default='memcheck',