By default Divi includes this right border in sidebars (widgets):

Divi Right Side Bar Border

Divi Right Side Bar Border

I find myself removing it on every install; so I finally added it to my default installation child-theme style.css file and am capturing the css required to remove it.

.et_pb_widget_area_left {
  border-right: none;
}

Et voila.

Divi Right Side Bar Border Removed

Divi Right Side Bar Border Removed