This iOS 9.0 availability check should have been removed as part of#4327. It is no longer needed now that the minimum iOS version is 9.0.

Part offlutter/flutter#84198

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 [relevant style guides] and ran [the auto-formatter]. (Note that unlike the flutter/flutter repo, the flutter/plugins repo does usedart format.)
• I signed the [CLA].
• The title of the PR starts with the name of the plugin surrounded by square brackets, e.g.[shared_preferences]
• I listed at least one issue that this PR fixes in the description above.
• Iupdated pubspec.yaml with an appropriate new version according to the [pub versioning philosophy].
• I updated CHANGELOG.md to add a description of the change.
• I updated/added relevant documentation (doc comments with///).
• I added new tests to check the change I am making or feature I am adding, or Hixie said the PR is test exempt.
• All existing and new tests are passing.