Remove deprecated Layer.findAll

[Piinks]

Description

This removes the deprecated findAll method from the Layer class that has reached the EOL .
Instead, users should call Layer.findAllAnnotations(...).annotations.

Part of deprecations that are slated for removal for next release in https://flutter.dev/go/deprecation-lifetime

More context: https://medium.com/flutter/deprecation-lifetime-in-flutter-e4d76ee738ad

Related Issues

Deprecated in #42953
#73910

Checklist

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• I read the Contributor Guide and followed the process outlined there for submitting PRs.
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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.

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[darrenaustin]

LGTM

[Piinks]

This is waiting on a fuchsia roll