Issue #3497493 by pdureau, grimreaper: Clean variant logic in templates

components/accordion/accordion.twig

components/alert/alert.twig

components/button/button.twig

components/button_group/button_group.twig

components/card/card.twig

components/carousel/carousel.twig

components/close_button/close_button.twig

components/list/list.twig

components/list_group/list_group.twig

components/list_group_item/list_group_item.twig

components/modal/modal.twig

components/nav/nav.twig

components/navbar/navbar.twig

components/navbar_nav/navbar_nav.twig

components/offcanvas/offcanvas.twig

components/pagination/pagination.twig

components/progress/progress.twig

components/spinner/spinner.twig

components/table/table.twig

components/table_cell/table_cell.twig