Revert "[css-viewport] Define the viewport property in window (#10548)" (#10566)

This reverts commit e462f14.

Author: chrishtr

css-viewport/Overview.bs

@@ -362,27 +362,8 @@ only the value previously set to it.
 }
 </pre>
 
-<h2 id=extensions-to-the-window-interface>Extensions to the {{Window}} Interface</h2>
-
-<pre class=idl>
-partial interface Window {
-[SameObject, Replaceable] readonly attribute Viewport? viewport;
-};
-</pre>
-
-<h2 id=viewport>Viewport</h2>
-
-<h3 id="the-viewport-interface">The {{Viewport}} Interface</h3>
-
-<pre class=idl>
-[Exposed=Window]
-interface Viewport : EventTarget {
-  readonly attribute double zoom;
-};
-</pre>
-
-<h2 id='zoom'>
-	The <dfn attribute for=Viewport>zoom</dfn> property
+<h2 id='zoom-property'>
+	The 'zoom' property
 </h2>
 
 An element becomes zoomed when the 'zoom' property has a positive computed value different than 1