style: Remove PseudoElement::inherits_all.

I plan to change servo to use all: inherit on its UA sheet.

I hope the patch below should make it good enough performance-wise. And also,
it's probably broken so I don't think it's worth supporting it specially.

Differential Revision: https://phabricator.services.mozilla.com/D8686

components/style/properties/properties.mako.rs

@@ -3298,15 +3298,6 @@ impl<'a> StyleBuilder<'a> {
         let reset_style = device.default_computed_values();
         let inherited_style = parent_style.unwrap_or(reset_style);
         let inherited_style_ignoring_first_line = parent_style_ignoring_first_line.unwrap_or(reset_style);
-        // FIXME(bz): inherits_all seems like a fundamentally broken idea.  I'm
-        // 99% sure it should give incorrect behavior for table anonymous box
-        // backgrounds, for example.  This code doesn't attempt to make it play
-        // nice with inherited_style_ignoring_first_line.
-        let reset_style = if pseudo.map_or(false, |p| p.inherits_all()) {
-            inherited_style
-        } else {
-            reset_style
-        };
 
         let flags = inherited_style.flags.inherited();