Remove ReEmpty

compiler/rustc_typeck/src/outlives/utils.rs

@@ -161,12 +161,6 @@ fn is_free_region(region: Region<'_>) -> bool {
         // ignore it.  We can't put it on the struct header anyway.
         ty::ReLateBound(..) => false,
 
-        // This can appear in `where Self: ` bounds (#64855):
-        //
-        //     struct Bar<T>(<Self as Foo>::Type) where Self: ;
-        //     struct Baz<'a>(&'a Self) where Self: ;
-        ty::ReEmpty(_) => false,
-
         // These regions don't appear in types from type declarations:
         ty::ReErased | ty::ReVar(..) | ty::RePlaceholder(..) | ty::ReFree(..) => {
             bug!("unexpected region in outlives inference: {:?}", region);

compiler/rustc_typeck/src/variance/constraints.rs

@@ -411,11 +411,7 @@ impl<'a, 'tcx> ConstraintContext<'a, 'tcx> {
                 // way early-bound regions do, so we skip them here.
             }
 
-            ty::ReFree(..)
-            | ty::ReVar(..)
-            | ty::RePlaceholder(..)
-            | ty::ReEmpty(_)
-            | ty::ReErased => {
+            ty::ReFree(..) | ty::ReVar(..) | ty::RePlaceholder(..) | ty::ReErased => {
                 // We don't expect to see anything but 'static or bound
                 // regions when visiting member types or method types.
                 bug!(