Bug 1599675 [wpt PR 20469] - Mark idlharness tests for fetch/xhr as slow, a=testonly

Bug 1599675 [wpt PR 20469] - Mark idlharness tests for fetch/xhr as slow, a=testonly

Automatic update from web-platform-tests
Mark idlharness tests for fetch/xhr as slow

They depend on dom/html which is slow. Also remove entries from
TestExpectations because they are covered either by
 - the long timeout introduced here, or
 - MSAN related expectations (see https://crbug.com/856601)

Bug: 1026151, 990900, 856601
Change-Id: I094590d485c318fef5ab4c2e213a621211a6a3a1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1936444
Commit-Queue: Yutaka Hirano <yhirano@chromium.org>
Auto-Submit: Yutaka Hirano <yhirano@chromium.org>
Reviewed-by: Hiroki Nakagawa <nhiroki@chromium.org>
Cr-Commit-Position: refs/heads/master@{#719517}

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wpt-commits: 8321e0c262cfc7e247b0ae01839f5a7095afe59f
wpt-pr: 20469