Use a trait instead of the now disallowed missing trait there

Author: spastorino

src/test/ui/type-alias-impl-trait/unused_generic_param.rs

@@ -1,16 +1,17 @@
+// check-pass
+
 #![feature(type_alias_impl_trait)]
+#![allow(dead_code)]
 
 fn main() {}
 
-type PartiallyDefined<T> = impl 'static;
-//~^ ERROR: at least one trait must be specified
+type PartiallyDefined<T> = impl Sized;
 
 fn partially_defined<T: std::fmt::Debug>(_: T) -> PartiallyDefined<T> {
     4u32
 }
 
-type PartiallyDefined2<T> = impl 'static;
-//~^ ERROR: at least one trait must be specified
+type PartiallyDefined2<T> = impl Sized;
 
 fn partially_defined2<T: std::fmt::Debug>(_: T) -> PartiallyDefined2<T> {
     4u32