refactor(compiler): remove all source-level traces to tsc-wrapped (#18966)

- temporarily keeps the old sources under packages/tsc-wrapped
  until the build scripts are changed to use compiler-cli everywhere.
- removes the compiler options `disableTransformerPipeline` that was introduced
  in a previous beta of Angular 5, i.e. the transformer based compiler
  is now always enabled.

PR Close #18966

packages/compiler-cli/test/aot_host_spec.ts

@@ -6,7 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {ModuleMetadata} from '@angular/tsc-wrapped';
+import {ModuleMetadata} from '@angular/compiler-cli/src/metadata/index';
 import * as ts from 'typescript';
 
 import {CompilerHost} from '../src/compiler_host';