Editorial: Remove accname step numbers from accessibility WPTs

[rahimabdi]

For clearer and more maintainable test documentation, @cookiecrook @spectranaut @jnurthen discussed on Apr 8 (SF-based ARIA F2F meeting) removing accname step numbers from accessibility test documentation.

For example, the labelledby accname computation step tests reference Step 2H (https://github.com/web-platform-tests/wpt/blob/459d38f305/accname/name/comp_labelledby.html):

<!-- Step 2H: Recursive Name from Content, see wpt/accname/name/comp_name_from_content.html  -->
<h3>
  <a href="#" aria-labeledby="nested_image_label2">
    link1<!-- this text is skipped because of aria-labeledby -->
  </a>
  <a href="#" data-expectedlabel="link2 image link3" data-testname="link name from content for each child including nested image (referenced elsewhere via labeledby)" class="ex">
    link2
    <img id="nested_image_label2" alt="image" src="data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACH5BAEAAAAALAAAAAABAAEAAAICRAEAOw==">
    <!-- image skipped in this link (when computing heading text) because it was already referenced by the first link within this heading label recursion cycle. -->
    <!-- but image not skipped when computing the text of the link itself since it has not been referenced in that context -->
    link3
  </a>
</h3>