Remove references to local app admin view

[alecmerdler]

What does this PR do?

The local app '/admin' route is being removed because it does
not provide any value, so we need to remove references from it
in the CLI.

Does your PR introduce any breaking changes? If yes, please list them.

• When running locally with lightning run app, the /admin route is no longer available

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[alecmerdler]

@awaelchli Since I'm not a maintainer, not all of the CI tests will pass for this PR. Are you able to force-merge it for me?

[awaelchli]

Oh @alecmerdler, you are pushing it from a fork. If you had created the branch directly on this repo, it would have been possible to run all CI jobs. We are still waiting for #13927. None of us can force merge anything. Only admin can. So I will ask admin :)