Remove UA styles for h1 in article, aside, nav, and section

https://bugs.webkit.org/show_bug.cgi?id=292765

Reviewed by NOBODY (OOPS!).

Firefox has rolled this out to 5% of its release audience as of 138,
100% of the beta audience, and plans to ship this in 140 which is now
riding the trains.

Chrome has also taken steps in deprecating this pattern and plans to
fast follow Firefox.

I think we should do the same.

For testing I removed a redundant local test and imported a PR that
will be merged once the specification change goes in:
web-platform-tests/wpt#51673

Author: annevk

LayoutTests/fast/css/h1-in-section-elements.html

@@ -12,18 +12,12 @@
   display: block;
 }
 
-h1 { margin-block-start: 0.67em; margin-block-end: 0.67em; font-size: 2.00em; font-weight: bold; }
-h2 { margin-block-start: 0.83em; margin-block-end: 0.83em; font-size: 1.50em; font-weight: bold; }
-h3 { margin-block-start: 1.00em; margin-block-end: 1.00em; font-size: 1.17em; font-weight: bold; }
-h4 { margin-block-start: 1.33em; margin-block-end: 1.33em; font-size: 1.00em; font-weight: bold; }
-h5 { margin-block-start: 1.67em; margin-block-end: 1.67em; font-size: 0.83em; font-weight: bold; }
-h6 { margin-block-start: 2.33em; margin-block-end: 2.33em; font-size: 0.67em; font-weight: bold; }
-
-:is(article, aside, nav, section) h1 { margin-block-start: 0.83em; margin-block-end: 0.83em; font-size: 1.50em; }
-:is(article, aside, nav, section) :is(article, aside, nav, section) h1 { margin-block-start: 1.00em; margin-block-end: 1.00em; font-size: 1.17em; }
-:is(article, aside, nav, section) :is(article, aside, nav, section) :is(article, aside, nav, section) h1 { margin-block-start: 1.33em; margin-block-end: 1.33em; font-size: 1.00em; }
-:is(article, aside, nav, section) :is(article, aside, nav, section) :is(article, aside, nav, section) :is(article, aside, nav, section) h1 { margin-block-start: 1.67em; margin-block-end: 1.67em; font-size: 0.83em; }
-:is(article, aside, nav, section) :is(article, aside, nav, section) :is(article, aside, nav, section) :is(article, aside, nav, section) :is(article, aside, nav, section) h1 { margin-block-start: 2.33em; margin-block-end: 2.33em; font-size: 0.67em; }
+h1 { margin-block: 0.67em; font-size: 2.00em; font-weight: bold; }
+h2 { margin-block: 0.83em; font-size: 1.50em; font-weight: bold; }
+h3 { margin-block: 1.00em; font-size: 1.17em; font-weight: bold; }
+h4 { margin-block: 1.33em; font-size: 1.00em; font-weight: bold; }
+h5 { margin-block: 1.67em; font-size: 0.83em; font-weight: bold; }
+h6 { margin-block: 2.33em; font-size: 0.67em; font-weight: bold; }
 
 </style>