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"Split and Defer" action

![screenshot of split_and_defer transition](/uploads/2a9d4efc139b881bfec82a425996c659/image.png)

functionality can be achieved with "Solve Divergences" action with a "Split and Defer" 

![screenshot of solve_divergence transition choosing split and defer action](/uploads/704c4713d842455c4e369a99d8f4867a/image.png)

we don't need two ways of doing the same thing.

This removes the workflow transitions and the dialogs and update the tests to use the "Solve Divergences" action instead.

See merge request nexedi/erp5!1148