layout-2020: build fixes.

components/style/values/generics/length.rs

@@ -207,15 +207,6 @@ impl<LengthPercentage> MaxSize<LengthPercentage> {
     pub fn none() -> Self {
         MaxSize::None
     }
-
-    /// Convert
-    #[cfg(not(feature = "gecko"))]
-    pub fn to_option(self) -> Option<LengthPercentage> {
-        match self {
-            Self::LengthPercentage(lp) => Some(lp),
-            Self::None => None,
-        }
-    }
 }
 
 /// A generic `<length>` | `<number>` value for the `-moz-tab-size` property.