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/transformers/lower_expressions_spec.ts

@@ -6,9 +6,9 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {ModuleMetadata} from '@angular/tsc-wrapped';
 import * as ts from 'typescript';
 
+import {ModuleMetadata} from '../../src/metadata/index';
 import {LowerMetadataCache, LoweringRequest, RequestLocationMap, getExpressionLoweringTransformFactory} from '../../src/transformers/lower_expressions';
 import {Directory, MockAotContext, MockCompilerHost} from '../mocks';