refactor(@angular-devkit/build-angular): remove unused getEsVersionForFileName helper

The `getEsVersionForFileName` helper function was previously used for recently removed differential loading support but is now unused and can also be removed.

Author: clydin

packages/angular_devkit/build_angular/src/webpack/utils/helpers.ts

@@ -7,7 +7,6 @@
  */
 
 import * as path from 'path';
-import { ScriptTarget } from 'typescript';
 import { Configuration, SourceMapDevToolPlugin } from 'webpack';
 import { ExtraEntryPoint, ExtraEntryPointClass } from '../../builders/browser/schema';
 
@@ -93,24 +92,6 @@ export function getSourceMapDevTool(
   });
 }
 
-/**
- * Returns an ES version file suffix to differentiate between various builds.
- */
-export function getEsVersionForFileName(
-  scriptTarget: ScriptTarget | undefined,
-  esVersionInFileName = false,
-): string {
-  if (!esVersionInFileName || scriptTarget === undefined) {
-    return '';
-  }
-
-  if (scriptTarget === ScriptTarget.ESNext) {
-    return '-esnext';
-  }
-
-  return '-' + ScriptTarget[scriptTarget].toLowerCase();
-}
-
 export function isPolyfillsEntry(name: string): boolean {
   return name === 'polyfills';
 }