LibWeb: Remove weird is_undefined_or_auto() helper in FFC

This was a leftover from when ComputedValues stored sizes in Optionals.
Now that we've gotten rid of the "undefined" state, there's no need for
this helper, we can just access the size values directly.

Userland/Libraries/LibWeb/Layout/FlexFormattingContext.cpp

@@ -35,13 +35,6 @@ static float get_pixel_size(FormattingState const& state, Box const& box, Option
     return length_percentage->resolved(box, inner_main_size).to_px(box);
 }
 
-static bool is_undefined_or_auto(Optional<CSS::LengthPercentage> const& length_percentage)
-{
-    if (!length_percentage.has_value())
-        return true;
-    return length_percentage->is_length() && length_percentage->length().is_auto();
-}
-
 FlexFormattingContext::FlexFormattingContext(FormattingState& state, Box const& flex_container, FormattingContext* parent)
     : FormattingContext(Type::Flex, state, flex_container, parent)
     , m_flex_container_state(m_state.get_mutable(flex_container))
@@ -306,14 +299,14 @@ float FlexFormattingContext::resolved_definite_main_size(Box const& box) const
 
 bool FlexFormattingContext::has_main_min_size(Box const& box) const
 {
-    auto value = is_row_layout() ? box.computed_values().min_width() : box.computed_values().min_height();
-    return !is_undefined_or_auto(value);
+    auto const& value = is_row_layout() ? box.computed_values().min_width() : box.computed_values().min_height();
+    return !value.is_auto();
 }
 
 bool FlexFormattingContext::has_cross_min_size(Box const& box) const
 {
-    auto value = is_row_layout() ? box.computed_values().min_height() : box.computed_values().min_width();
-    return !is_undefined_or_auto(value);
+    auto const& value = is_row_layout() ? box.computed_values().min_height() : box.computed_values().min_width();
+    return !value.is_auto();
 }
 
 bool FlexFormattingContext::has_definite_cross_size(Box const& box) const
@@ -344,16 +337,14 @@ float FlexFormattingContext::specified_cross_min_size(Box const& box) const
 
 bool FlexFormattingContext::has_main_max_size(Box const& box) const
 {
-    return is_row_layout()
-        ? !is_undefined_or_auto(box.computed_values().max_width())
-        : !is_undefined_or_auto(box.computed_values().max_height());
+    auto const& value = is_row_layout() ? box.computed_values().max_width() : box.computed_values().max_height();
+    return !value.is_auto();
 }
 
 bool FlexFormattingContext::has_cross_max_size(Box const& box) const
 {
-    return is_row_layout()
-        ? !is_undefined_or_auto(box.computed_values().max_height())
-        : !is_undefined_or_auto(box.computed_values().max_width());
+    auto const& value = !is_row_layout() ? box.computed_values().max_width() : box.computed_values().max_height();
+    return !value.is_auto();
 }
 
 float FlexFormattingContext::specified_main_max_size(Box const& box) const