STYLE: Remove virtual from ElastixBase elxGet and elxSet macro's
STYLE: Remove virtual from ElastixBase elxGet and elxSet macro's

Following the documentation, which already said:

> they are not virtual, since for now we do not need to override them somewhere

SuperElastix/elastix,SuperElastix/elastix,SuperElastix/elastix,SuperElastix/elastix,SuperElastix/elastix