Remove superfluous test setup

There are no zones at the start of the test. This is probably a
left-over from old times when specs were not encapsulated in
transactions.

spec/system/admin/configuration/zones_spec.rb

@@ -8,7 +8,6 @@ describe "Zones" do
 
   before do
     login_as_admin
-    Spree::Zone.delete_all
   end
 
   it "list existing zones" do