fix: make the update command behave similar to the logic before 6.0.0

[DimitarTachev]

PR Checklist

• The PR title follows our guidelines: https://github.com/NativeScript/NativeScript/blob/master/CONTRIBUTING.md#commit-messages.
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What is the current behavior?

The update command is updating all dependencies from the project templates but it doesn't call their update scripts.

What is the new behavior?

The update command is updating only the core-modules and the runtimes as it was before 6.0.0