[css-ui] Remove slider-horizontal, square-button, push-button from <compat-auto>

Fixes w3c#8506

Author: zcorpan

css-ui-4/Overview.bs

@@ -2094,7 +2094,7 @@ where CSS can be used to restyle them.
 		for earlier non-standard versions of this property.
 		They all have the same effect as ''appearance/auto''.
 
-		<pre class=prod style="white-space: normal"><<compat-auto>> =  <dfn>searchfield</dfn> | <dfn>textarea</dfn> | <dfn>push-button</dfn> | <dfn>slider-horizontal</dfn> | <dfn>checkbox</dfn> | <dfn>radio</dfn> | <dfn>square-button</dfn> | <dfn>menulist</dfn> | <dfn>listbox</dfn> | <dfn>meter</dfn> | <dfn>progress-bar</dfn> | <dfn>button</dfn> </pre>
+		<pre class=prod style="white-space: normal"><<compat-auto>> =  <dfn>searchfield</dfn> | <dfn>textarea</dfn> | <dfn>checkbox</dfn> | <dfn>radio</dfn> | <dfn>menulist</dfn> | <dfn>listbox</dfn> | <dfn>meter</dfn> | <dfn>progress-bar</dfn> | <dfn>button</dfn> </pre>
 
 		Issue: When ''appearance/auto'' is widely supported,
 		recommend using it instead.