Bug 1870926 [wpt PR 43734] - Remove experimental ::details-summary pseudo-element...

Bug 1870926 [wpt PR 43734] - Remove experimental ::details-summary pseudo-element., a=testonly

Automatic update from web-platform-tests
Remove experimental ::details-summary pseudo-element.

Developers can already style the <summary> element.  Being able to style
a pseudo-element that wraps only the <summary> element has little value
and appears to add substantial confusion.  (It does slightly improve the
ability to style the default summary when no summary is provided, but
not necessarily in useful ways.)

Bug: 1469418
Change-Id: Ia0c9bfd61696e5ca46e4ab3113e7bc45fde88bf4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5137042
Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Auto-Submit: David Baron <dbaron@chromium.org>
Commit-Queue: David Baron <dbaron@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1239642}

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wpt-commits: cf0e998b161ad83360079ed86a51cf3f18836711
wpt-pr: 43734