Remove scroll-margin test expectations for Win7

virtual/threaded/external/wpt/css/css-scroll-snap/scroll-margin.html was
failing because the expected output file for Win7 was not deleted.

Bug: 964239
Change-Id: Ie49db2682d1e0148e60a03bea8f752165d2b1d9b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1821824
Commit-Queue: Kaan Alsan <alsan@google.com>
Reviewed-by: Majid Valipour <majidvp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#699385}

third_party/blink/web_tests/TestExpectations

@@ -2160,7 +2160,6 @@ crbug.com/983789 [ Win7 ] http/tests/cookies/js-set-null.html [ Pass Failure ]
 crbug.com/983788 http/tests/cookies/http-get-cookie-set-in-js.html [ Pass Failure ]
 crbug.com/983788 http/tests/cookies/same-site/popup-cross-site.https.html [ Pass Timeout ]
 crbug.com/984438 external/wpt/css/css-scroll-snap/snap-at-user-scroll-end-manual.html [ Failure Pass ]
-crbug.com/964239 [ Win7 ] virtual/threaded/external/wpt/css/css-scroll-snap/scroll-margin.html [ Failure ]
 crbug.com/984467 virtual/gpu/fast/canvas/canvas-composite-stroke-alpha.html [ Pass Timeout ]
 
 ### sheriff 2018-05-28

third_party/blink/web_tests/platform/win7/virtual/threaded/external/wpt/css/css-scroll-snap/scroll-margin-expected.txt

-This is a testharness.js-based test.
-PASS Snaps to the positions adjusted by scroll-margin
-FAIL scroll-margin doesn't contribute to the snap position of the element if it's outside of the scroll port assert_equals: expected 0 but got 400
-Harness: the test ran to completion.
-