[5.6] Fix: revert model syncing after soft-delete

[edbentinck]

This reverts the changes made in PR #24400

Why?
By immediately syncing the original model array, you could no longer retrieve changed values from the 'deleted' model event. This differs from the behavior of other model events such as 'created' and 'updated'.

Since you can manually call syncOriginal anyway, it seems it would be more desirable to leave the behavior of deleted in line with the other model events than to break this behavior for everyone without offering an opt-out:

$userModel->delete();
$userModel->syncOriginal();
$userModel->restore();

Tests
I have left in the tests from the previous PR and just added the manual syncing to show that those cases are still supported. By all means I can remove them.

If required I can also add some tests to ensure that changes on the model can be accessed after deleting.

Let me know.