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_infer/src/infer/region_constraints/leak_check.rs

@@ -358,14 +358,12 @@ impl<'tcx> SccUniverse<'tcx> {
 
 rustc_index::newtype_index! {
     #[debug_format = "LeakCheckNode({})"]
-    struct LeakCheckNode {
-    }
+    struct LeakCheckNode {}
 }
 
 rustc_index::newtype_index! {
     #[debug_format = "LeakCheckScc({})"]
-    struct LeakCheckScc {
-    }
+    struct LeakCheckScc {}
 }
 
 /// Represents the graph of constraints. For each `R1: R2` constraint we create