refactor: stop reexporting transformer from index.js

This won't work for projects that don't have dependency for
`@ngtools/webpack`.

Author: sis0k0

Diff for: index.js

@@ -10,7 +10,6 @@ const {
 
 Object.assign(exports, require("./plugins"));
 Object.assign(exports, require("./host/resolver"));
-Object.assign(exports, require("./transformers/ns-replace-bootstrap"));
 
 exports.getAotEntryModule = function (appDirectory) {
 	verifyEntryModuleDirectory(appDirectory);

Diff for: transformers/ns-replace-bootstrap.ts

@@ -7,7 +7,7 @@ import {
     insertStarImport,
     ReplaceNodeOperation,
     makeTransform
-} from "@ngtools/webpack/src/transformers"
+} from "@ngtools/webpack/src/transformers";
 import { workaroundResolve } from '@ngtools/webpack/src/compiler_host';
 import { AngularCompilerPlugin } from '@ngtools/webpack';