Enable quotes property (#110)

Signed-off-by: Xiaocheng Hu <xiaochengh.work@gmail.com>

Author: xiaochengh

style/properties/longhands/list.mako.rs

@@ -69,7 +69,6 @@ ${helpers.predefined_type(
     "Quotes",
     "computed::Quotes::get_initial_value()",
     engines="gecko servo",
-    servo_pref="layout.legacy_layout",
     animation_type="discrete",
     spec="https://drafts.csswg.org/css-content/#propdef-quotes",
     servo_restyle_damage="rebuild_and_reflow",