[FIX] point_of_sale: confirm and error popup style

Style of some popups is broken because of the removal of absolute
positioning of the dialog footer. We now remove the absolute
popup height and let the content of the popup body dictate the
height of the popup.

addons/point_of_sale/static/src/css/pos.css

@@ -2493,7 +2493,6 @@ td {
     margin: auto;
     max-width:500px;
     width: 100%;
-    height:400px;
     text-align:center;
     font-size:20px;
     font-weight:bold;
@@ -2515,13 +2514,6 @@ td {
     height: auto;
 }
 
-.pos .modal-dialog .popup-confirm{
-    height: 250px;
-}
-.pos .popup-confirm .body {
-    overflow: auto;
-    height: 120px;
-}
 .pos .popup .title {
     background: rgba(255,255,255,0.5);
     margin: 0;
@@ -2533,7 +2525,6 @@ td {
     font-weight: normal;
     font-size: 18px;
     margin: 16px;
-    margin-top: 20px;
 }
 
 .pos .popup-lg .body {