tooltip: Fix the placement of tooltip in group list.

When there is only one user group, the tooltip appears on the upper side
of the "group-row" and gets hidden.

This commit sets `overflow: visible` which is default value, causing the
tooltip position to invert when there is only one user group.

web/styles/subscriptions.css

@@ -675,7 +675,6 @@ h4.user_group_setting_subsection_title {
 .user-groups-list,
 .streams-list {
     position: relative;
-    overflow: auto;
     -webkit-overflow-scrolling: touch;
     width: 100%;
 }