Fix specificity of :not selector list downleveling

Author: devongovett

scripts/build-prefixes.js

@@ -594,6 +594,7 @@ let c = `// This file is autogenerated by build-prefixes.js. DO NOT EDIT!
 
 use crate::targets::Browsers;
 
+#[allow(dead_code)]
 #[derive(Clone, Copy, PartialEq)]
 pub enum Feature {
   ${[...compat.keys()].flat().map(enumify).sort().join(',\n  ')}

src/compat.rs

@@ -2,6 +2,7 @@
 
 use crate::targets::Browsers;
 
+#[allow(dead_code)]
 #[derive(Clone, Copy, PartialEq)]
 pub enum Feature {
   AbsFunction,