Don't link to specific WHATWG multipage page

"Links to the multipage version of the specification are unfortunately
likely to break over time."
-- https://html.spec.whatwg.org/multipage/asefij.html

This commit removes all references to the specific pages when viewing
WHATWG using multipage mode. I went through all these links and they
redirect fine.

Regex used to generate this commit:

`s_whatwg.org/multipage/.*#_whatwg.org/multipage/#_g`

components/script/dom/workernavigator.rs

@@ -11,7 +11,7 @@ use dom::navigatorinfo;
 use dom::workerglobalscope::WorkerGlobalScope;
 use util::str::DOMString;
 
-// https://html.spec.whatwg.org/multipage/workers.html#workernavigator
+// https://html.spec.whatwg.org/multipage/#workernavigator
 #[dom_struct]
 pub struct WorkerNavigator {
     reflector_: Reflector,