Remove deprecated [PointerEnterEvent, PointerExitEvent].fromHoverEvent

[Piinks]

Description

This removes the deprecated PointerEnterEvent.fromHoverEvent and PointerExitEvent.fromHoverEvent. Instances of these methods should be replaced by fromMouseEvent.

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 #28602

Tests

Tests for quick fix tool.

Checklist

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• All existing and new tests are passing.
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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.

[flutter-dashboard]

It looks like this pull request may not have tests. Please make sure to add tests before merging. If you need an exemption to this rule, contact Hixie on the #hackers channel in Chat.

Reviewers: Read the Tree Hygiene page and make sure this patch meets those guidelines before LGTMing.

[goderbauer]

LGTM