chore: disable preview

[rigor789]

PR Checklist

• The PR title follows our guidelines: https://github.com/NativeScript/NativeScript/blob/master/CONTRIBUTING.md#commit-messages.
• There is an issue for the bug/feature this PR is for. To avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it.
• You have signed the CLA.
• All existing tests are passing: https://github.com/NativeScript/nativescript-cli/blob/master/CONTRIBUTING.md#contribute-to-the-code-base
• Tests for the changes are included.

What is the current behavior?

What is the new behavior?

Fixes/Implements/Closes #[Issue Number].

[Krzysiek555]

Is there any information why actually the preview option has been disabled?

[rigor789]

@Krzysiek555 the current version hasn't been updated, as we are transitioning the infrastructure (it will be made available again in the near future).