Revert "Validate resolution for SelfCtor too."

compiler/rustc_resolve/src/diagnostics.rs

@@ -550,7 +550,7 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
 
                 let sm = self.tcx.sess.source_map();
                 let def_id = match outer_res {
-                    Res::SelfTyParam { .. } | Res::SelfCtor(_) => {
+                    Res::SelfTyParam { .. } => {
                         err.span_label(span, "can't use `Self` here");
                         return err;
                     }

compiler/rustc_resolve/src/ident.rs

@@ -1174,10 +1174,7 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
                     return Res::Err;
                 }
             }
-            Res::Def(DefKind::TyParam, _)
-            | Res::SelfTyParam { .. }
-            | Res::SelfTyAlias { .. }
-            | Res::SelfCtor(_) => {
+            Res::Def(DefKind::TyParam, _) | Res::SelfTyParam { .. } | Res::SelfTyAlias { .. } => {
                 for rib in ribs {
                     let has_generic_params: HasGenericParams = match rib.kind {
                         RibKind::Normal

tests/ui/self/self-ctor-nongeneric.rs

@@ -0,0 +1,15 @@
+// `Self` as a constructor is currently allowed when the outer item is not generic.
+// check-pass
+
+struct S0(usize);
+
+impl S0 {
+    fn foo() {
+        const C: S0 = Self(0);
+        fn bar() -> S0 {
+            Self(0)
+        }
+    }
+}
+
+fn main() {}