Fix NLL test

Author: estebank

src/test/ui/in-band-lifetimes/mismatched_trait_impl.nll.stderr

@@ -1,25 +1,14 @@
-error[E0495]: cannot infer an appropriate lifetime for lifetime parameter 'a in generic type due to conflicting requirements
+error: `impl` item signature doesn't match `trait` item signature
   --> $DIR/mismatched_trait_impl.rs:9:5
    |
+LL |     fn foo(&self, x: &'a u32, y: &u32) -> &'a u32;
+   |     ---------------------------------------------- expected fn(&i32, &'a u32, &u32) -> &'a u32
+...
 LL |     fn foo(&self, x: &u32, y: &'a u32) -> &'a u32 {
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ found fn(&i32, &u32, &u32) -> &u32
    |
-note: first, the lifetime cannot outlive the anonymous lifetime #2 defined on the method body at 9:5...
-  --> $DIR/mismatched_trait_impl.rs:9:5
-   |
-LL | /     fn foo(&self, x: &u32, y: &'a u32) -> &'a u32 {
-LL | |         x
-LL | |     }
-   | |_____^
-note: ...but the lifetime must also be valid for the lifetime `'a` as defined on the method body at 9:32...
-  --> $DIR/mismatched_trait_impl.rs:9:32
-   |
-LL |     fn foo(&self, x: &u32, y: &'a u32) -> &'a u32 {
-   |                                ^^
-   = note: ...so that the method type is compatible with trait:
-           expected fn(&i32, &'a u32, &u32) -> &'a u32
-              found fn(&i32, &u32, &u32) -> &u32
+   = note: expected `fn(&i32, &'a u32, &u32) -> &'a u32`
+              found `fn(&i32, &u32, &u32) -> &u32`
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0495`.