Drop the dead title-bar batch-actions block instead of varying it

The previous commit claimed to fix "only one of eight identical
`padding: 10px 20px` rules was extracted" by applying the new variables to
`#title_bar #titlebar_right div.batch_actions_selector` as well. That rule
matches nothing: ActiveAdmin renders the batch-actions selector only inside
`div.table_tools` — `build_table_tools` in
lib/active_admin/views/pages/index.rb, unchanged across 3.0 through 3.5 —
so the title bar never contains one.

The claim came from a hand-written screenshot harness whose markup I had
invented, with a batch-actions button sitting inside `#titlebar_right`.
Shooting the same scenario against a generated ActiveAdmin admin showed the
real markup and the mistake with it.

So there is no second button beside the title-bar action button to disagree
with, `$skinTitleBarButtonPadding*` on `.action_item a` is complete as it
stands, and the block this removes has been dead CSS for the whole supported
ActiveAdmin range. The two live copies under `div.table_tools` keep their
literal padding: they are a different row, and giving them a variable named
for the title bar would be worse than leaving them alone.

Author: Fivell

app/assets/stylesheets/wigu/active_admin_theme.scss

@@ -272,21 +272,6 @@ body.active_admin {
           }
         }
       }
-      div.batch_actions_selector {
-        a {
-          background-image: none;
-          border: none;
-          box-shadow: none;
-          background-color: $skinMainSecondColor;
-          @include rounded($skinBorderRadius);
-          border: none;
-          padding: $skinTitleBarButtonPaddingY $skinTitleBarButtonPaddingX;
-          color: #ffffff;
-          &:hover {
-            background-color: lighten( $skinMainSecondColor, 5% );
-          }
-        }
-      }
     }
   }
   .flashes {