Cut distracting statement about external resources

The section of the spec that provide details about attributes for the
link element contains the following statement:

> Some of the attributes control whether or not the external resource is
> to be applied (as defined below).

This change drops that statement.

That statement has been in the spec for 11 years but isn’t stating a
normative requirement nor serving any useful purpose—instead, it’s
actually just distracting and counter-productive in that despite saying
“as defined below”, the notion of “to be applied” isn’t actually clearly
defined at all in the prose anywhere in the spc below that statement.

Fixes whatwg#2503.

source

@@ -12956,9 +12956,8 @@ interface <dfn>HTMLLinkElement</dfn> : <span>HTMLElement</span> {
   link's location within the document.</p>
 
   <p>The exact behavior for <span data-x="external resource link">links to external resources</span>
-  depends on the exact relationship, as defined for the relevant <a href="#linkTypes">link type</a>.
-  Some of the attributes control whether or not the external resource is to be applied (as defined
-  below).</p>
+  depends on the exact relationship, as defined for the relevant <a href="#linkTypes">link
+  type</a>.</p>
 
   <p>The <dfn><code data-x="attr-link-media">media</code></dfn> attribute says which media the
   resource applies to. The value must be a <span>valid media query list</span>.</p>