Remove WidgetInspectorService setPubRootDirectories deprecations

[Piinks]

Part of #139243

setPubRootDirectories is replaced by the addPubRootDirectories method.
Deprecated in #106567

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the Flutter Style Guide, including Features we expect every widget to implement.
• I signed the CLA.
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is test-exempt.
• All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel on Discord.

[Piinks]

@CoderDake can you take a look at this PR? The migration of setPubRootDirectories -> addPubRootDirectories breaks 100s of tests. Was the deprecation message wrong?

This is from #106567

[Piinks]

For now, this is blocked on

• Migration is not working
• Apply dart fixes to mixins dart-lang/sdk#46465
• [dart fix] inEnum does not apply transform dart-lang/sdk#54188

[flutter-dashboard]

This pull request has been changed to a draft. The currently pending flutter-gold status will not be able to resolve until a new commit is pushed or the change is marked ready for review again.

For more guidance, visit Writing a golden file test for package:flutter.

Reviewers: Read the Tree Hygiene page and make sure this patch meets those guidelines before LGTMing.