Fixes #12683: Remove the overflow: hidden; from the .panel-group > .panel...

Fixes #12683: Remove the overflow: hidden; from the .panel-group > .panel because it apparently serves no purpose and cuts off nested dropdown menus.

dist/css/bootstrap-rtl.css

@@ -6213,7 +6213,6 @@ a.list-group-item-danger.active:focus {
 
 .panel-group .panel {
   margin-bottom: 0;
-  overflow: hidden;
   border-radius: 4px;
 }
 

dist/css/bootstrap.css

@@ -5003,7 +5003,6 @@ a.list-group-item-danger.active:focus {
 }
 .panel-group .panel {
   margin-bottom: 0;
-  overflow: hidden;
   border-radius: 4px;
 }
 .panel-group .panel + .panel {

less/panels.less

@@ -199,7 +199,6 @@
   .panel {
     margin-bottom: 0;
     border-radius: @panel-border-radius;
-    overflow: hidden; // crop contents when collapsed
     + .panel {
       margin-top: 5px;
     }