style: Use Rust types for some misc properties.

-moz-tab-size, border-image-outset and border-image-slice.

This is not a particularly interesting patch, just removes some code. We can
remove way more code when a few related properties are also ported.

Differential Revision: https://phabricator.services.mozilla.com/D19825

components/style/values/computed/text.rs

@@ -10,7 +10,6 @@ use crate::values::computed::length::{Length, LengthPercentage};
 use crate::values::computed::{NonNegativeLength, NonNegativeNumber};
 use crate::values::generics::text::InitialLetter as GenericInitialLetter;
 use crate::values::generics::text::LineHeight as GenericLineHeight;
-use crate::values::generics::text::MozTabSize as GenericMozTabSize;
 use crate::values::generics::text::Spacing;
 use crate::values::specified::text::TextOverflowSide;
 use crate::values::specified::text::{TextEmphasisFillMode, TextEmphasisShapeKeyword};
@@ -124,9 +123,6 @@ impl TextDecorationsInEffect {
     }
 }
 
-/// A specified value for the `-moz-tab-size` property.
-pub type MozTabSize = GenericMozTabSize<NonNegativeNumber, NonNegativeLength>;
-
 /// computed value for the text-emphasis-style property
 #[derive(Clone, Debug, MallocSizeOf, PartialEq, ToCss)]
 pub enum TextEmphasisStyle {