[url_launcher] Re-remove Android API<24 support

[stuartmorgan-g]

This re-lands the url_launcher_android portion of #9851, which was reverted in #9986, but with the missing min SDK update this time.

Part of flutter/flutter#170807

Pre-Review Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• 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 updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy, or I have commented below to indicate which version change exemption this PR falls under¹.
• I updated CHANGELOG.md to add a description of the change, following repository CHANGELOG style, or I have commented below to indicate which CHANGELOG exemption this PR falls under¹.
• 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 under¹.
• All existing and new tests are passing.

Footnotes

1. Regular contributors who have demonstrated familiarity with the repository guidelines only need to comment if the PR is not auto-exempted by repo tooling. ↩ ↩² ↩³

[flutter-dashboard]

It looks like this pull request may not have tests. Please make sure to add tests or get an explicit test exemption before merging.

If you are not sure if you need tests, consider this rule of thumb: the purpose of a test is to make sure someone doesn't accidentally revert the fix. Ask yourself, is there anything in your PR that you feel it is important we not accidentally revert back to how it was before your fix?

Reviewers: Read the Tree Hygiene page and make sure this patch meets those guidelines before LGTMing. If you believe this PR qualifies for a test exemption, contact "@test-exemption-reviewer" in the #hackers channel in Discord (don't just cc them here, they won't see it!). The test exemption team is a small volunteer group, so all reviewers should feel empowered to ask for tests, without delegating that responsibility entirely to the test exemption group.

[gemini-code-assist]

Code Review

This pull request correctly re-implements the removal of support for Android API levels below 24 by updating the minSdkVersion and cleaning up related obsolete code. The changes are logical and well-contained. I've identified one minor issue in the CHANGELOG.md file regarding the formatting of a retracted version entry, which should be adjusted to align with the repository's style guide.

[gemini-code-assist]

According to the repository's CHANGELOG style guide, when a version is retracted, the content should be replaced with a single bullet point explaining the retraction. The original change notes for the retracted version should be removed.¹

Style Guide References

Footnotes

1. For a version that is retracted, the version header should be kept, but the content should be replaced with a single bullet point: * **Retracted** for (reason). ↩

[stuartmorgan-g]

I love that it added a footnote to try to make this hallucination sound more convincing.

[bparrishMines]

LGTM