fix(@angular/pwa): remove `@schematics/angular` utility deep import usage
fix(@angular/pwa): remove `@schematics/angular` utility deep import usage

Workspace helper utilties are now exported from `@schematics/angular/utility`.
The previously used deep imports are not considered part of the public API and may change in any version.

clydin/angular-cli,angular/angular-cli,clydin/angular-cli,geofffilippi/angular-cli,angular/angular-cli,angular/angular-cli,geofffilippi/angular-cli,geofffilippi/angular-cli,angular/angular-cli,clydin/angular-cli,geofffilippi/angular-cli,clydin/angular-cli