[css-flexbox] Remove passing gap test

Mozilla changed the test in their repo and it got pulled down as part of
a wpt sync.

Bug: 762679
Change-Id: Ief73dc47bf3f8f0bfe47de30d1be34f497018325
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2216280Reviewed-by: Stephen Chenney <schenney@chromium.org>
Commit-Queue: David Grogan <dgrogan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#771936}

third_party/blink/web_tests/TestExpectations

@@ -1149,8 +1149,6 @@ crbug.com/846557 [ Mac ] virtual/layout_ng_flex_box/css3/flexbox/button.html [ F
 crbug.com/1066859 external/wpt/css/css-flexbox/position-absolute-009.html [ Failure ]
 
 # Fail in both legacy flex and NG flex
-crbug.com/762679 external/wpt/css/vendor-imports/mozilla/mozilla-central-reftests/flexbox/flexbox-column-row-gap-004.html [ Failure ]
-
 crbug.com/626703 virtual/layout_ng_flex_box/external/wpt/css/vendor-imports/mozilla/mozilla-central-reftests/flexbox/flexbox-align-self-baseline-horiz-008.xhtml [ Failure ]
 
 # Fieldset in NG