Fix: subtitle should be undefined by default

Author: sfe-efficy

src/components/BCard/BCardBody.vue

@@ -34,7 +34,6 @@ interface BCardBodyProps {
 const props = withDefaults(defineProps<BCardBodyProps>(), {
   bodyTag: 'div',
   overlay: false,
-  subTitle: 'h4',
   titleTag: 'h4',
 })