A few small cleanups for newtype_index

Remove the `..` from the body, only a few invocations used it and it's
inconsistent with rust syntax.

Use `;` instead of `,` between consts. As the Rust syntax gods inteded.

compiler/rustc_passes/src/liveness.rs

@@ -109,14 +109,12 @@ mod rwu_table;
 
 rustc_index::newtype_index! {
     #[debug_format = "v({})"]
-    pub struct Variable {
-    }
+    pub struct Variable {}
 }
 
 rustc_index::newtype_index! {
     #[debug_format = "ln({})"]
-    pub struct LiveNode {
-    }
+    pub struct LiveNode {}
 }
 
 #[derive(Copy, Clone, PartialEq, Debug)]