chore(ensureValidRuntimeType): remove special v16 error message (#4183)

Author: yaacovCR

src/execution/__tests__/abstract-test.ts

@@ -633,15 +633,7 @@ describe('Execute: Handles execution of abstract types', () => {
     // @ts-expect-error
     assertInterfaceType(schema.getType('Pet')).resolveType = () => [];
     expectError({ forTypeName: undefined }).toEqual(
-      'Abstract type "Pet" must resolve to an Object type at runtime for field "Query.pet" with value { __typename: undefined }, received "[]".',
-    );
-
-    // FIXME: workaround since we can't inject resolveType into SDL
-    // @ts-expect-error
-    assertInterfaceType(schema.getType('Pet')).resolveType = () =>
-      schema.getType('Cat');
-    expectError({ forTypeName: undefined }).toEqual(
-      'Support for returning GraphQLObjectType from resolveType was removed in graphql-js@16.0.0 please return type name instead.',
+      'Abstract type "Pet" must resolve to an Object type at runtime for field "Query.pet" with value { __typename: undefined }, received "[]", which is not a valid Object type name.',
     );
   });
 });

src/execution/execute.ts

@@ -1588,18 +1588,12 @@ function ensureValidRuntimeType(
     );
   }
 
-  // releases before 16.0.0 supported returning `GraphQLObjectType` from `resolveType`
-  // TODO: remove in 17.0.0 release
-  if (isObjectType(runtimeTypeName)) {
-    throw new GraphQLError(
-      'Support for returning GraphQLObjectType from resolveType was removed in graphql-js@16.0.0 please return type name instead.',
-    );
-  }
-
   if (typeof runtimeTypeName !== 'string') {
     throw new GraphQLError(
       `Abstract type "${returnType}" must resolve to an Object type at runtime for field "${info.parentType}.${info.fieldName}" with ` +
-        `value ${inspect(result)}, received "${inspect(runtimeTypeName)}".`,
+        `value ${inspect(result)}, received "${inspect(
+          runtimeTypeName,
+        )}", which is not a valid Object type name.`,
     );
   }