Remove confusing display option from admin

Thanks daimrod & cécile :)

hardware_provisioning/admin.py

@@ -42,7 +42,6 @@ class AvailabilityFilter(admin.SimpleListFilter):
     def lookups(self, request, model_admin):
         return [
             ('available', 'Disponible'),
-            ('unavailable', 'Indispo (emprunté ou déployé)'),
             ('borrowed', 'Emprunté'),
             ('deployed', 'Déployé'),
         ]
@@ -50,8 +49,6 @@ class AvailabilityFilter(admin.SimpleListFilter):
     def queryset(self, request, queryset):
         if self.value() == 'available':
             return queryset.available()
-        elif self.value() == 'unavailable':
-            return queryset.unavailable()
         elif self.value() == 'borrowed':
             return queryset.borrowed()
         elif self.value() == 'deployed':