Remove flaky expectations for CSS variable tests

Now that the web font timing issue for WPT in Blink has been fixed
(https://crbug.com/507054), these tests should no longer be flaky.
Remove the expectations.

Bug: 582836
Change-Id: I88f94b0f9133c8c787a358f00f06a76382e7d26e
Reviewed-on: https://chromium-review.googlesource.com/962704Reviewed-by: Koji Ishii <kojii@chromium.org>
Commit-Queue: Robert Ma <robertma@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543524}

third_party/WebKit/LayoutTests/TestExpectations

@@ -1332,12 +1332,6 @@ crbug.com/553838 external/wpt/css/vendor-imports/mozilla/mozilla-central-reftest
 # We paint in an incorrect order when layers are present
 crbug.com/370604 external/wpt/css/vendor-imports/mozilla/mozilla-central-reftests/flexbox/flexbox-paint-ordering-002.xhtml [ Failure ]
 
-crbug.com/582836 external/wpt/css/vendor-imports/mozilla/mozilla-central-reftests/variables/variable-declaration-15.html [ Failure Pass ]
-crbug.com/582836 external/wpt/css/vendor-imports/mozilla/mozilla-central-reftests/variables/variable-declaration-16.html [ Failure Pass ]
-crbug.com/582836 external/wpt/css/vendor-imports/mozilla/mozilla-central-reftests/variables/variable-declaration-17.html [ Failure Pass ]
-crbug.com/582836 external/wpt/css/vendor-imports/mozilla/mozilla-central-reftests/variables/variable-declaration-18.html [ Failure Pass ]
-crbug.com/582836 external/wpt/css/vendor-imports/mozilla/mozilla-central-reftests/variables/variable-external-font-face-01.html [ Pass Failure ]
-
 crbug.com/736319 external/wpt/css/vendor-imports/mozilla/mozilla-central-reftests/writing-modes-3/text-combine-upright-break-inside-001a.html [ Failure ]
 crbug.com/736319 external/wpt/css/vendor-imports/mozilla/mozilla-central-reftests/writing-modes-3/text-combine-upright-compression-001.html [ Failure ]
 crbug.com/736319 external/wpt/css/vendor-imports/mozilla/mozilla-central-reftests/writing-modes-3/text-combine-upright-compression-002.html [ Failure ]