build: remove references to tsc-wrapped (#19298)

With this commit `ngc` is used instead of `tsc-wrapped` for
collecting metadata and tsickle rewriting and `tsc-wrapped`
is removed from the repository.

`@angular/tsc-wrapped@5` is now deprecated and is no longer
used, updated, or maintained as part as of Angular 5.x.x.

`@angular/tsc-wrapped@4` is still maintained and required by
Angular 4.x.x and will be maintained as long as 4.x.x is in
LTS.

PR Close #19298

packages/compiler/testing/index.ts

@@ -11,4 +11,4 @@
 // replaces this file with production index.ts when it rewrites private symbol
 // names.
 
-export * from './public_api';
+export * from './testing';