Remove "support ElementInternals" reflection flag

Fixes #11516.

Author: lukewarlow

source

@@ -8036,17 +8036,6 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
   means that the IDL attribute getter returns the current value of the content attribute, and the
   setter changes the value of the content attribute to the given value.</p>
 
-  <p>If the <span>reflected target</span> is an element, then the <span>reflected IDL
-  attribute</span> can additionally declare to <dfn>support <code>ElementInternals</code></dfn>.
-  This means that the <code>ElementInternals</code> interface also has a <span>reflected IDL
-  attribute</span>, with the same identifier, and that <span>reflected IDL attribute</span> <span
-  data-x="reflect">reflects</span> the same <span>reflected content attribute name</span>.</p>
-
-  <p class="example" id="example-reflect-incantation">The <code data-x=""><var>fooBar</var></code>
-  IDL attribute <!--non-normative-->must <span>reflect</span> the <code
-  data-x=""><var>foobar</var></code> content attribute and <span>support
-  <code>ElementInternals</code></span>.</p>
-
   <div w-nodev>
 
   <p><span data-x="reflected target">Reflected targets</span> have these associated algorithms:
@@ -8511,8 +8500,8 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
   <p>If a <span>reflected IDL attribute</span> has the type <code>DOMTokenList</code>, then its
   getter steps are to return a <code>DOMTokenList</code> object whose associated element is
   <span>this</span> and associated attribute's local name is the <span>reflected content
-  attribute name</span>. Specification authors cannot use <span>support
-  <code>ElementInternals</code></span> for IDL attributes of this type.</p>
+  attribute name</span>. Specification authors cannot reflect IDL attributes of this type on
+  <code>ElementInternals</code>.</p>
   <!-- Supporting ElementInternals is doable in theory, but would require corresponding changes to
        DOMTokenList. -->