[local_auth] Update README.md

[RafaRuiz]

Update README.md into from recent changes !5309

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]. (Unlike the flutter/flutter repo, the flutter/plugins repo does use dart 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.
• I updated pubspec.yaml with an appropriate new version according to the [pub versioning philosophy], or this PR is [exempt from version changes].
• I updated CHANGELOG.md to add a description of the change, [following repository CHANGELOG style].
• 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.

[stuartmorgan-g]

In the future, please don't just check all of the boxes without actually going through the checklist. You've indicated that you've updated the CHANGELOG and version, as would be required for this change, but have not actually done so.

However, the change itself here is incorrect; there is no getEnrolledBiometrics method in this package. #5309 neither changed this package, nor changed any Dart method names, so I'm not sure what motivated this PR.