Enable aspect-ratio for layout 2020 (#54)

Signed-off-by: valadaptive <[email protected]>

Author: valadaptive

style/properties/longhands/position.mako.rs

@@ -425,7 +425,6 @@ ${helpers.predefined_type(
     "AspectRatio",
     "computed::AspectRatio::auto()",
     engines="gecko servo",
-    servo_pref="layout.legacy_layout",
     animation_value_type="ComputedValue",
     spec="https://drafts.csswg.org/css-sizing-4/#aspect-ratio",
     servo_restyle_damage="reflow",