Since `versionedFiles` behaves in the exact same way as `files`, there
is no reaason to have both. Users should use `files` instead.
This commit deprecates the property and prints a warning when coming
across an asset-group that uses it. It should be completely removed in
a future version.
Note, it has also been removed from the default `ngsw-config.json`
template in angular/devkit#754.
PR Close#23584
Also, remove `plnkr.json` for `service-worker-getting-started` guide,
since it is not used and ServiceWorker cannot work correctly in
plnkr/stackblitz anyway (e.g. no build step to re-compute hashes).
A zipper might be useful and can be added in a subsequent PR, but it is
currently broken (e.g. no dependency on `@angular/service-worker`).
PR Close#20165