[css-ui] Remove Animation Origin for 'appearance' disabling (#7230)

Fixes #7215

Author: zcorpan

css-ui-4/Overview.bs

@@ -2204,10 +2204,10 @@ as a [=legacy name alias=] of 'appearance'.
 <h4 id="appearance-disabling-properties">
 Properties Disabling Native Appearance</h4>
 
-Certain properties, when declared in the [=Author Origin=] or [=Animation Origin=],
+Certain properties, when declared in the [=Author Origin=],
 will disable the [=native appearance=] of certain [=widgets=].
 Specifically,
-if all the declarations of the [=Author Origin=] and [=Animation Origin=]
+if all the declarations of the [=Author Origin=]
 pertaining to such a [=widget=] are cascaded
 and a [=cascaded value=] exists--
 and is not ''revert'' or ''revert-layer''--