Change some tests to use the shorter comment style

src/test/ui/associated-types/cache/project-fn-ret-contravariant.rs

@@ -47,6 +47,4 @@ fn transmute<'a,'b>(x: &'a u32, y: &'b u32) -> (&'a u32, &'b u32) {
 }
 
 #[rustc_error]
-fn main() { }
-//[ok]~^ ERROR fatal error triggered by #[rustc_error]
-//[oneuse]~^^ ERROR fatal error triggered by #[rustc_error]
+fn main() { } //[ok,oneuse]~ ERROR fatal error triggered by #[rustc_error]

src/test/ui/error-codes/E0161.rs

@@ -20,14 +20,8 @@
 
 fn foo(x: Box<[i32]>) {
     box *x;
-    //[migrate]~^ ERROR E0161
-    //[nll]~^^ ERROR E0161
-    //[zflags]~^^^ ERROR E0161
-    //[edition]~^^^^ ERROR E0161
-    //[migrateul]~^^^^^ ERROR E0161
-    //[nllul]~^^^^^^ ERROR E0161
-    //[zflagsul]~^^^^^^^ ERROR E0161
-    //[editionul]~^^^^^^^^ ERROR E0161
+    //[migrate,nll,zflags,edition]~^ ERROR E0161
+    //[migrateul,nllul,zflagsul,editionul]~^^ ERROR E0161
 }
 
 fn main() {}

src/test/ui/underscore-lifetime/where-clause-inherent-impl-underscore.rs

@@ -11,8 +11,7 @@ struct Foo<T> {
 impl<T> Foo<T>
 where
     T: WithRegion<'_>
-//[rust2015]~^ ERROR `'_` cannot be used here
-//[rust2018]~^^ ERROR `'_` cannot be used here
+//[rust2015,rust2018]~^ ERROR `'_` cannot be used here
 { }
 
 fn main() {}

src/test/ui/underscore-lifetime/where-clause-trait-impl-region.rs

@@ -9,8 +9,7 @@ trait Foo { }
 impl<T> Foo for Vec<T>
 where
     T: WithType<&u32>
-//[rust2015]~^ ERROR `&` without an explicit lifetime name cannot be used here
-//[rust2018]~^^ ERROR `&` without an explicit lifetime name cannot be used here
+//[rust2015,rust2018]~^ ERROR `&` without an explicit lifetime name cannot be used here
 { }
 
 fn main() {}

src/test/ui/underscore-lifetime/where-clause-trait-impl-underscore.rs

@@ -9,8 +9,7 @@ trait Foo { }
 impl<T> Foo for Vec<T>
 where
     T: WithRegion<'_>
-//[rust2015]~^ ERROR `'_` cannot be used here
-//[rust2018]~^^ ERROR `'_` cannot be used here
+//[rust2015,rust2018]~^ ERROR `'_` cannot be used here
 { }
 
 fn main() {}