LibWeb: Simplify getting resolved value for animation-duration

We now know that `animation_duration_computed_value` is always a
StyleValueList

Author: Calme1709

Libraries/LibWeb/CSS/CSSStyleProperties.cpp

@@ -880,14 +880,6 @@ RefPtr<StyleValue const> CSSStyleProperties::style_value_for_computed_property(L
         auto const& animation_duration_computed_value = get_computed_value(PropertyID::AnimationDuration);
 
         if (animation_timeline_computed_value.as_value_list().size() == 1 && animation_timeline_computed_value.as_value_list().values()[0]->to_keyword() == Keyword::Auto) {
-
-            // FIXME: We can remove these two branches once parse_comma_separated_value_list always returns StyleValueList.
-            if (animation_duration_computed_value.to_keyword() == Keyword::Auto)
-                return TimeStyleValue::create(Time::make_seconds(0));
-
-            if (!animation_duration_computed_value.is_value_list())
-                return animation_duration_computed_value;
-
             StyleValueVector resolved_durations;
 
             for (auto const& duration : animation_duration_computed_value.as_value_list().values()) {