Removes explicit setup calls from the plugin core. Each module now
registers its own save/load/cleanup steps via a static initializer,
decoupling them from InitSceneSwitcher and SwitcherData.
The steps added via AddPostLoadStep() from the copy were never executed.
Thus they might be invalid when RunPostLoadSteps() is next called.
This could result in a crash when a new action or condition is added
after e.g. a "Filter" action's TempVariableRef was copied, which adds a
PostLoadStep to resolve the macro segment reference.
