This PR removes the behavior that the number_field changes focus to the
previous element when using the decrement button.

I mainly noticed this while decreasing the tab-size of a language, since
it there closes the page...

Please note that I am unsure what if any purpose this code has.
I was unable to find a use case and since it is not present in the
`increment_handler` I guess it should never have been here

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Release Notes:

* Fixed wrongly focus previous element on number_field decrement