Remove FlutterApplication from app templates.

[hpoul]

Description

There is an inconsistency between the migration guide for pre flutter 1.12 android applications: https://github.com/flutter/flutter/wiki/Upgrading-pre-1.12-Android-projects and the current app templates.

According to the guide (for both, Full-Flutter app migration as well as for Add-to-app migration):

3. Remove the reference to FlutterApplication from the application tag.

This PR removes FlutterApplication from AndroidManifest.xml to make it consistent with manually upgraded projects.

Related Issues

• No issue which would be fixed

Tests

No tests, as this does not add any functionality.

Checklist

Before you create this PR, confirm that it meets all requirements listed below by checking the relevant checkboxes ([x]). This will ensure a smooth and quick review process.

• I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
• I signed the [CLA].
• I read and followed the [Flutter Style Guide], including [Features we expect every widget to implement].
• I read the [Tree Hygiene] wiki page, which explains my responsibilities.
• I updated/added relevant documentation (doc comments with ///).
• All existing and new tests are passing.
• The analyzer (flutter analyze --flutter-repo) does not report any problems on my PR.
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

Did any tests fail when you ran them? Please read [Handling breaking changes].

• No, no existing tests failed, so this is not a breaking change.

[xster]

Reminds me I need to merge flutter/engine#20769 (since this inadvertently hides a problem flutter/engine#20769 fixes) . Let's merge this after our next branch cut next week.

[xster]

This LGTM. flutter/engine#20769 is merged as well.

Please wait until Sept 14th before merging this.

[jonahwilliams]

@xster September 14th of this year, right? :)

[xster]

Thanks for reminding Jonah! Merge on green.