style: Remove prefers-color-scheme: no-preference.

It was removed from the spec.

Differential Revision: https://phabricator.services.mozilla.com/D78834

components/style/gecko/media_features.rs

@@ -278,13 +278,18 @@ enum PrefersReducedMotion {
     Reduce,
 }
 
+fn color_scheme_no_preference_enabled(_: &crate::parser::ParserContext) -> bool {
+    static_prefs::pref!("layout.css.prefers-color-scheme-no-preference.enabled")
+}
+
 /// Values for the prefers-color-scheme media feature.
 #[derive(Clone, Copy, Debug, FromPrimitive, Parse, PartialEq, ToCss)]
 #[repr(u8)]
 #[allow(missing_docs)]
 pub enum PrefersColorScheme {
     Light,
     Dark,
+    #[parse(condition = "color_scheme_no_preference_enabled")]
     NoPreference,
 }