Update tests which reference E0421

Author: tiehuis

src/test/compile-fail/issue-21221-2.rs

@@ -27,5 +27,5 @@ pub mod baz {
 struct Foo;
 impl T for Foo { }
 //~^ ERROR trait `T` is not in scope
-//~| HELP you can to import it into scope: `use foo::bar::T;`.
+//~| HELP you can import it into scope: `use foo::bar::T;`.
 //~| HELP run `rustc --explain E0405` to see a detailed explanation

src/test/compile-fail/issue-21221-3.rs

@@ -24,7 +24,7 @@ struct Foo;
 // are hidden from the view.
 impl OuterTrait for Foo {}
 //~^ ERROR trait `OuterTrait` is not in scope
-//~| HELP you can to import it into scope: `use issue_21221_3::outer::OuterTrait;`.
+//~| HELP you can import it into scope: `use issue_21221_3::outer::OuterTrait;`.
 //~| HELP run `rustc --explain E0405` to see a detailed explanation
 fn main() {
     println!("Hello, world!");

src/test/compile-fail/issue-21221-4.rs

@@ -19,7 +19,7 @@ struct Foo;
 
 impl T for Foo {}
 //~^ ERROR trait `T` is not in scope
-//~| HELP you can to import it into scope: `use issue_21221_4::T;`.
+//~| HELP you can import it into scope: `use issue_21221_4::T;`.
 //~| HELP run `rustc --explain E0405` to see a detailed explanation
 
 fn main() {