Bug 1526626 [wpt PR 15181] - Drop nullable document.domain experiment…

…, a=testonly

Automatic update from web-platform-tests
Drop nullable document.domain experiment

This reverts https://crrev.com/7a5c7e067f550762 to retire the experiment
to allow `document.domain = null`.

Bug: 733150
Change-Id: I29304d26aafe90c5a6e0d5dc15704718772fc522
Reviewed-on: https://chromium-review.googlesource.com/c/1446265
Reviewed-by: Mike West <mkwstchromium.org>
Commit-Queue: Taiju Tsuiki <tzikchromium.org>
Cr-Commit-Position: refs/heads/master{#630218}

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wpt-commits: 0cb54ecc9cdf4f1a8b0d5641d9145ff59898e62b
wpt-pr: 15181

UltraBlame original commit: 4c0e3ef420b69ccc46071cd6aa83ea35b94907ad