rm unnecessary border-radius properties from .btn-group-vertical code

[skip sauce]
[skip validator]

scss/_button-group.scss

@@ -177,11 +177,9 @@
     border-radius: 0;
   }
   &:first-child:not(:last-child) {
-    border-top-right-radius: $btn-border-radius;
     @include border-bottom-radius(0);
   }
   &:last-child:not(:first-child) {
-    border-bottom-left-radius: $btn-border-radius;
     @include border-top-radius(0);
   }
 }