Layout 2020: Remove the floats preference

Enable floats always. It doesn't make sense to have this preference as
it's a basic feature of an experimental layout engine.

components/config/prefs.rs

@@ -445,9 +445,6 @@ mod gen {
                 flexbox: {
                     enabled: bool,
                 },
-                floats: {
-                    enabled: bool,
-                },
                 #[serde(default = "default_layout_threads")]
                 threads: i64,
                 viewport: {

components/style/properties/longhands/box.mako.rs

@@ -67,7 +67,6 @@ ${helpers.predefined_type(
     "computed::Float::None",
     engines="gecko servo-2013 servo-2020",
     initial_specified_value="specified::Float::None",
-    servo_2020_pref="layout.floats.enabled",
     spec="https://drafts.csswg.org/css-box/#propdef-float",
     animation_value_type="discrete",
     servo_restyle_damage="rebuild_and_reflow",
@@ -79,7 +78,6 @@ ${helpers.predefined_type(
     "Clear",
     "computed::Clear::None",
     engines="gecko servo-2013 servo-2020",
-    servo_2020_pref="layout.floats.enabled",
     animation_value_type="discrete",
     gecko_ffi_name="mBreakType",
     spec="https://drafts.csswg.org/css-box/#propdef-clear",