Optimise dedupe to skip install when nothing to dedupe

[jordanoverbye]

What's the problem this PR addresses?

Currently the dedupe command always runs project.installWithNewReport() even when no packages need deduplication, causing unnecessary installs and lockfile updates.

How did you fix it?

Exit early if no packages need deduping. Only run project.installWithNewReport() when necessary.

Checklist

• I have read the Contributing Guide.
• I have set the packages that need to be released for my changes to be effective.
• I will check that all automated PR checks pass before the PR gets reviewed.

[clemyan]

Only @yarnpkg/cli and @yarnpkg/plugin-essentials should be released. Other packages should be marked as declined.

LGTM, but I'd like to have a second pair of eyes to look over it.

[jordanoverbye]

Thank you for the review @clemyan! I've just pushed a change to the versions file so only @yarnpkg/cli and @yarnpkg/plugin-essentials should now be released.