Replace favicon.ico in favor of png in src/assets

### Bug Report or Feature Request (mark with an `x`)
```
- [ ] bug report -> please search issues before submitting
- [x] feature request
```

### Area
```
- [ ] devkit
- [x] schematics
```

### Desired functionality
favicon.ico is outdated and obsolete relic from the 90s. Browsers for the past 2decades have supported png favicons. Additionally, while it's fairly easy now to generate a favicon.ico, it's just not needed or used anymore.

There's no reason imo to include favicon.ico, even for "compatibility". Removing the favicon.ico will also remove the entries needed in angular.json and remove the only asset stored outside of src/assets.

It should be replaced in favor of modern favicon methods. PWAs should use manifest.json

```



```
Note: svg doesn't have full browser support.

We haven't needed favicon.ico in years, but it's still widely used and implemented, even though all browsers support modern methods.

まず、favicon を作成する schematic ファイルと angular.json 内の関連エントリを追跡し、次に src/assets を調べて現在のアイコンを確認します。生成されるアプリケーションに含めるべき最新の PNG またはマニフェストベースのファイルを確認し、古い favicon.ico 参照を削除して、生成されたアセットを対象としている場合は関連する schematic テストを更新します。

索引モデルが issue の本文から書いたものです。