Don't require associated types with Self: Sized bounds in dyn Trait objects

compiler/rustc_hir_analysis/src/astconv/mod.rs

@@ -1131,6 +1131,16 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             }
         }
 
+        for def_ids in associated_types.values_mut() {
+            for def_id in def_ids.clone() {
+                // If the associated type has a `where Self: Sized` bound, we do not need to constrain the associated
+                // type in the `dyn Trait`.
+                if tcx.generics_require_sized_self(def_id) {
+                    def_ids.remove(&def_id);
+                }
+            }
+        }
+
         self.complain_about_missing_associated_types(
             associated_types,
             potential_assoc_types,