Remove split view functionality

The Calligra split view functionality has some serious problems:

* we cannot split and have two documents in one view
* it is buggy
* the action list is loaded twice when splitting the view, which means
that all shortcuts stop working because they are duplicated

REVIEW:101993





We need to redesign this feature and implement it properly. The age-old
hacks (veryHackyActionList...) cannot be fixed, so remove the current
implementation.