Remove polyfill for 'flatMap' (graphql#2777)

src/type/validate.js

@@ -1,5 +1,4 @@
 import find from '../polyfills/find';
-import flatMap from '../polyfills/flatMap';
 import objectValues from '../polyfills/objectValues';
 
 import inspect from '../jsutils/inspect';
@@ -599,8 +598,12 @@ function getAllSubNodes<T: ASTNode, K: ASTNode, L: ASTNode>(
   object: SDLDefinedObject<T, K>,
   getter: (T | K) => ?(L | $ReadOnlyArray<L>),
 ): $ReadOnlyArray<L> {
-  // istanbul ignore next (See: 'https://github.com/graphql/graphql-js/issues/2203')
-  return flatMap(getAllNodes(object), (item) => getter(item) ?? []);
+  let subNodes = [];
+  for (const node of getAllNodes(object)) {
+    // istanbul ignore next (See: 'https://github.com/graphql/graphql-js/issues/2203')
+    subNodes = subNodes.concat(getter(node) ?? []);
+  }
+  return subNodes;
 }
 
 function getAllImplementsInterfaceNodes(

src/utilities/concatAST.js

@@ -1,15 +1,16 @@
-import flatMap from '../polyfills/flatMap';
-
 import type { DocumentNode } from '../language/ast';
 
 /**
  * Provided a collection of ASTs, presumably each from different files,
  * concatenate the ASTs together into batched AST, useful for validating many
  * GraphQL source files which together represent one conceptual application.
  */
-export function concatAST(asts: $ReadOnlyArray<DocumentNode>): DocumentNode {
-  return {
-    kind: 'Document',
-    definitions: flatMap(asts, (ast) => ast.definitions),
-  };
+export function concatAST(
+  documents: $ReadOnlyArray<DocumentNode>,
+): DocumentNode {
+  let definitions = [];
+  for (const doc of documents) {
+    definitions = definitions.concat(doc.definitions);
+  }
+  return { kind: 'Document', definitions };
 }