Be more permissive with required bounds on existential types

src/librustc_typeck/check/mod.rs

@@ -1385,10 +1385,7 @@ pub fn check_item_type<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, it: &'tcx hir::Ite
         }
         hir::ItemKind::Existential(..) => {
             let def_id = tcx.hir().local_def_id(it.id);
-            let pty_ty = tcx.type_of(def_id);
-            let generics = tcx.generics_of(def_id);
 
-            check_bounds_are_used(tcx, &generics, pty_ty);
             let substs = Substs::identity_for_item(tcx, def_id);
             check_opaque(tcx, def_id, substs, it.span);
         }

src/test/ui/existential_types/generic_duplicate_param_use.rs

@@ -1,8 +1,10 @@
+// compile-pass
 #![feature(existential_type)]
 
 fn main() {}
 
-existential type Two<T, U>: 'static; //~ ERROR type parameter `U` is unused
+// test that unused generic parameters are ok
+existential type Two<T, U>: 'static;
 
 fn one<T: 'static>(t: T) -> Two<T, T> {
     t

src/test/ui/existential_types/unused_generic_param.rs

@@ -1,15 +1,18 @@
+// compile-pass
 #![feature(existential_type)]
 
 fn main() {
 }
 
-existential type PartiallyDefined<T>: 'static; //~ `T` is unused
+// test that unused generic parameters are ok
+existential type PartiallyDefined<T>: 'static;
 
 fn partially_defined<T: std::fmt::Debug>(_: T) -> PartiallyDefined<T> {
     4u32
 }
 
-existential type PartiallyDefined2<T>: 'static; //~ `T` is unused
+// test that unused generic parameters are ok
+existential type PartiallyDefined2<T>: 'static;
 
 fn partially_defined2<T: std::fmt::Debug>(_: T) -> PartiallyDefined2<T> {
     4u32