[cupertino_ui] Remove unused parameters from constructors of generic classes.

[srawlins]

We already don't allow unused parameters from non-generic classes. There was a bug preventing us from reporting such parameters on generic classes.

This is work towards dart-lang/sdk#47839.

Pre-Review Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the AI contribution guidelines and understand my responsibilities, or I am not using AI tools.
• I read the Tree Hygiene page, which explains my responsibilities.
• I read and followed the relevant style guides and ran the auto-formatter.
• I signed the CLA.
• The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]
• I linked to at least one issue that this PR fixes in the description above.
• I followed the version and CHANGELOG instructions, using semantic versioning and the repository CHANGELOG style, or I have commented below to indicate which documented exception this PR falls under[^1].
• I updated/added any relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or I have commented below to indicate which test exemption this PR falls under[^1].
• All existing and new tests are passing.

Test exempt, as this code is covered by existing static and runtime checks.

[gemini-code-assist]

Code Review

This pull request removes unused super.key and super.settings parameters from the constructors of several private classes within the cupertino_ui package, specifically in context_menu.dart, route.dart, segmented_control.dart, and sheet.dart. There are no review comments to address, and no further feedback is provided.