refactor(testing): remove deprecated testing functions (#10832)

Remove TestComponentBuilder, addProviders, and withProviders. These
were deprecated in rc5 - see the changelog for update information.

Note - this does not actually remove the functions, but makes them
internal only. They will be removed from the codebase entirely
at a later time.

modules/@angular/core/testing.ts

@@ -9,7 +9,6 @@
 export * from './testing/async';
 export * from './testing/component_fixture';
 export * from './testing/fake_async';
-export * from './testing/test_component_builder';
 export * from './testing/test_bed';
 export * from './testing/testing';
 export * from './testing/metadata_override';