LibWeb/CSS: Remove unused ProductOperation enum

Author: https://github.com/AtkinsSJ
Commit: 2192868a0e
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/2966

Libraries/LibWeb/CSS/StyleValues/CalculatedStyleValue.h

@@ -42,10 +42,6 @@ public:
         Add,
         Subtract,
     };
-    enum class ProductOperation {
-        Multiply,
-        Divide,
-    };
 
     using PercentageBasis = Variant<Empty, Angle, Flex, Frequency, Length, Time>;