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_query_system/src/dep_graph/serialized.rs

@@ -28,8 +28,7 @@ use smallvec::SmallVec;
 // and use those bits to encode which index type it contains.
 rustc_index::newtype_index! {
     #[max = 0x7FFF_FFFF]
-    pub struct SerializedDepNodeIndex {
-    }
+    pub struct SerializedDepNodeIndex {}
 }
 
 /// Data for use when recompiling the **current crate**.