Revert "sheriff: Disable devtools accessibility tests"

This reverts commit fe3aa7f1.

Reason for revert: Original culprit for the failing tests has been reverted: https://chromium-review.googlesource.com/c/chromium/src/+/1806414

Original change's description:
> sheriff: Disable devtools accessibility tests
> 
> Tests are failing on linux:
> 
> https://ci.chromium.org/p/chromium/builders/ci/Linux%20Tests%20%28dbg%29%281%29/83157
> 
> TBR=pfeldman@chromium.org
> 
> Bug: 1004150
> Change-Id: I4bf6d6a10d60c7659a23b6aba1884a5995957531
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1804709
> Reviewed-by: Giovanni Ortuño Urquidi <ortuno@chromium.org>
> Commit-Queue: Giovanni Ortuño Urquidi <ortuno@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#696729}

TBR=pfeldman@chromium.org,ortuno@chromium.org

Change-Id: I24340b26d513d1013077eca1189003e55824f7e5
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1004150
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1804476Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#696748}

third_party/blink/web_tests/TestExpectations

@@ -6209,11 +6209,3 @@ 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 ]
-
-# Sheriff 2019-09-16
-crbug.com/1004150 [ Linux ] http/tests/devtools/a11y-axe-core/basic-a11y-test.js [ Pass Failure ]
-crbug.com/1004150 [ Linux ] http/tests/devtools/a11y-axe-core/console-a11y-test.js [ Pass Failure ]
-crbug.com/1004150 [ Linux ] http/tests/devtools/a11y-axe-core/elements/dom-breakpoints-a11y-test.js [ Pass Failure ]
-crbug.com/1004150 [ Linux ] http/tests/devtools/a11y-axe-core/memory/heap-profiler-a11y-test.js [ Pass Failure ]
-crbug.com/1004150 [ Linux ] http/tests/devtools/a11y-axe-core/quick-open-a11y-test.js [ Pass Failure ]
-crbug.com/1004150 [ Linux ] http/tests/devtools/a11y-axe-core/sources/dom-breakpoints-pane-a11y-test.js [ Pass Failure ]