Delete obsolete code

assets/admin.py

@@ -1,4 +1,5 @@
 from django.contrib import admin
+from reversion.admin import VersionAdmin
 from assets import models as assets
 
 
@@ -15,13 +16,13 @@ class AssetStatusAdmin(admin.ModelAdmin):
 
 
 @admin.register(assets.Supplier)
-class SupplierAdmin(admin.ModelAdmin):
+class SupplierAdmin(VersionAdmin):
     list_display = ['id', 'name']
     ordering = ['id']
 
 
 @admin.register(assets.Asset)
-class AssetAdmin(admin.ModelAdmin):
+class AssetAdmin(VersionAdmin):
     list_display = ['id', 'asset_id', 'description', 'category', 'status']
     list_filter = ['is_cable', 'category']
     search_fields = ['id', 'asset_id', 'description']