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/test_bed.ts

@@ -429,13 +429,6 @@ export class InjectSetupWrapper {
   }
 }
 
-/**
- * @deprecated Use `TestBed.configureTestingModule instead.
- */
-export function withProviders(providers: () => any) {
-  return new InjectSetupWrapper(() => { return {providers: providers()}; });
-}
-
 /**
  * @experimental
  */