[sensor] Mark flaky tests on Mac10.13 debug bots

Following tests are still flaky on Mac10.13 builders:

- external/wpt/gyroscope/Gyroscope.https.html
- external/wpt/accelerometer/Accelerometer.https.html
- external/wpt/orientation-sensor/AbsoluteOrientationSensor.https.html
- external/wpt/orientation-sensor/RelativeOrientationSensor.https.html

And remove external/wpt/accelerometer/LinearAccelerationSensor-shake-threshold-manual.https-expected.txt
which is unnecessary as it has already been in web_tests/NeverFixTests file.

Bug: 731018
Change-Id: I7cdd26682981e07695d9928536be3cbc0fca7890
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1808390Reviewed-by: Raphael Kubo da Costa <raphael.kubo.da.costa@intel.com>
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Commit-Queue: Raphael Kubo da Costa <raphael.kubo.da.costa@intel.com>
Cr-Commit-Position: refs/heads/master@{#697176}

third_party/blink/web_tests/TestExpectations

@@ -6204,3 +6204,7 @@ crbug.com/1003055 virtual/threaded/external/wpt/css/css-scroll-snap/scroll-targe
 
 # Sheriff 2019-09-12
 crbug.com/1003268 [ Win10 ] fast/harness/internals-observe-gc.html [ Failure ]
+crbug.com/731018 [ Mac10.13 Debug ] external/wpt/accelerometer/Accelerometer.https.html [ Pass Failure ]
+crbug.com/731018 [ Mac10.13 Debug ] external/wpt/gyroscope/Gyroscope.https.html [ Pass Failure ]
+crbug.com/731018 [ Mac10.13 Debug ] external/wpt/orientation-sensor/AbsoluteOrientationSensor.https.html [ Pass Failure ]
+crbug.com/731018 [ Mac10.13 Debug ] external/wpt/orientation-sensor/RelativeOrientationSensor.https.html [ Pass Failure ]

third_party/blink/web_tests/external/wpt/accelerometer/LinearAccelerationSensor-shake-threshold-manual.https-expected.txt

-This is a testharness.js-based test.
-FAIL Test that when shaking gesture along x axis of the device, the shake threshold can be greater than 25 assert_unreached: NotAllowedError:Permissions to access sensor are not granted Reached unreachable code
-Harness: the test ran to completion.
-