chore(example-app): remove data-example-app

[pawel-twardziak]

Closes #4586

PR Checklist

Please check if your PR fulfills the following requirements:

• [x] The commit message follows our guidelines: https://github.com/ngrx/platform/blob/main/CONTRIBUTING.md#commit
• [ ] Tests for the changes have been added (for bug fixes / features)
• [ ] Documentation has been added / updated (for bug fixes / features)

PR Type

It removes an obsolete app which is data-example-app

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[x] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

data-example-app is a project within the repo

Closes #4586

What is the new behavior?

data-example-app is removed

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

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