[css-values] Multiplication/division can't fail, since percent hint is always null.

Author: tabatkins

css-values-4/Overview.bs

@@ -1769,20 +1769,16 @@ Type Checking</h4>
 		Otherwise, the sub-expression's [=CSSNumericValue/type=] is the returned type.
 
 	* At a <css>*</css> sub-expression,
-		attempt to [=multiply two types|multiply the types=] of the left and right arguments.
-		If this returns failure,
-		the entire [=math function=] is invalid.
-		Otherwise, the sub-expression's [=CSSNumericValue/type=] is the returned type.
+		[=multiply two types|multiply the types=] of the left and right arguments.
+		The sub-expression's [=CSSNumericValue/type=] is the returned result.
 
 	* At a <css>/</css> sub-expression,
 		let |left type| be the result of finding the [=CSSNumericValue/types=] of its left argument,
 		and |right type| be the result of finding the [=CSSNumericValue/types=] of its right argument
 		and then [=invert a type|inverting=] it.
 
-		Attempt to [=multiply two types|multiply=] the |left type| and |right type|.
-		If this returns failure,
-		the entire [=math function=] is invalid.
-		Otherwise, the sub-expression's [=CSSNumericValue/type=] is the returned type.
+		The sub-expression's [=CSSNumericValue/type=] is the result of
+		[=multiply two types|multiplying=] the |left type| and |right type|.
 
 	* Anything else is a terminal value,
 		whose [=CSSNumericValue/type=] is determined based on its CSS type: