Allow <a>/<area> with download="" to not require user activation

Fixes #2116, wherein it is documented that this restriction is not
supported in any existing engines and attempting to do so in WebKit
proved not web-compatible.

Also helps with #1431.

source

@@ -18507,28 +18507,6 @@ interface <dfn>HTMLAnchorElement</dfn> : <span>HTMLElement</span> {
  <!-- https://software.hixie.ch/utilities/js/live-dom-viewer/?saved=2033 -->
  <!-- https://www.hixie.ch/tests/adhoc/html/navigation/iframe/002.html -->
 
- <li>
-
- <p>If either the <code>a</code> element has a <code
- data-x="attr-hyperlink-download">download</code> attribute and the algorithm is not
- <span>triggered by user activation</span>; or, if the user has not indicated a specific
- <span>browsing context</span> for following the link, and the element's <code
- data-x="attr-hyperlink-target">target</code> attribute is present, and applying <span>the rules
- for choosing a browsing context given a browsing context name</span>, using the value of the
- <code data-x="attr-hyperlink-target">target</code> attribute as the browsing context name, would
- result in there not being a chosen browsing context, then run these substeps:</p>
-
- <ol>
-
- <li><p>If there is an <span>entry settings object</span>, throw an
- <span>"<code>InvalidAccessError</code>"</span> <code>DOMException</code>.</p></li>
-
- <li><p>Abort these steps without following the hyperlink.</p></li>
-
- </ol>
-
- </li>
-
  <li><p>If the target of the <code data-x="event-click">click</code> event is an <code>img</code>
  element with an <code data-x="attr-img-ismap">ismap</code> attribute specified, then server-side
  image map processing must be performed, as follows:</p>
@@ -37347,28 +37325,6 @@ interface <dfn>HTMLAreaElement</dfn> : <span>HTMLElement</span> {
  <li><p>If the <code>area</code> element's <span>node document</span> is not <span>fully active</span>,
  then abort these steps.</p></li>
 
- <li>
-
- <p>If the <code>area</code> element has a <code data-x="attr-hyperlink-download">download</code>
- attribute and the algorithm is not <span>triggered by user activation</span>; or, if the user
- has not indicated a specific <span>browsing context</span> for following the link, and the
- element's <code data-x="attr-hyperlink-target">target</code> attribute is present, and applying
- <span>the rules for choosing a browsing context given a browsing context name</span>, using the
- value of the <code data-x="attr-hyperlink-target">target</code> attribute as the browsing
- context name, would result in there not being a chosen browsing context, then run these
- substeps:</p>
-
- <ol>
-
- <li><p>If there is an <span>entry settings object</span>, throw an
- <span>"<code>InvalidAccessError</code>"</span> <code>DOMException</code>.</p></li>
-
- <li><p>Abort these steps without following the hyperlink.</p></li>
-
- </ol>
-
- </li>
-
  <li><p>Otherwise, the user agent must <span data-x="following hyperlinks">follow the
  hyperlink</span> or <span data-x="downloading hyperlinks">download the hyperlink</span> created
  by the <code>area</code> element, if any, and as determined by the <code