Avoid calling MakePremiumPerAccess twice (bug 890044)

As weird as it seems, removing that whole part solves the issue because
the price is already updated during the creation process just above
during the `bango_account_list_form.save()` call.
Merge pull request #1143 from davidbgk/890044-avoid-double-call

Avoid calling MakePremiumPerAccess twice (bug 890044)