build(aio): remove -- from more yarn commands

[gkalpak]

PR Checklist

• The commit message follows our guidelines: https://github.com/angular/angular/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

[x] Build related changes

What is the current behavior?

Yarn commands unnecessarily invoked with --.

What is the new behavior?

Yarn commands invoked without --.

Does this PR introduce a breaking change?

[ ] Yes
[x] No

[mary-poppins]

You can preview 1088175 at https://pr19421-1088175.ngbuilds.io/.

[petebacondarwin]

Will there be another PR for stable?

[gkalpak]

That was the plan 😃 This doesn't merge cleanly into stable, because the run-example-e2e script has changed. I was waiting for #19369 to see what's left to remove across the whole repo.

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