(bug) fix errors due to sidekiq upgrade

- NoMethodError: undefined method 'delay' for UsersMailer:Class
- Removed open_api_calls_count_tracings fixtures due to the removal of the related table

app/services/members/members_service.rb

@@ -46,7 +46,7 @@ class Members::MembersService
         @member.update_statistic_profile
         @member.generate_subscription_invoice(current_user.id)
         @member.send_confirmation_instructions
-        UsersMailer.delay.notify_user_account_created(@member, @member.password)
+        UsersMailer.notify_user_account_created(@member, @member.password).deliver_later
         true
       else
         false

app/services/user_service.rb

@@ -46,7 +46,7 @@ class UserService
       admin.send_confirmation_instructions
       admin.add_role(:admin)
       admin.remove_role(:member)
-      UsersMailer.delay.notify_user_account_created(admin, generated_password)
+      UsersMailer.notify_user_account_created(admin, generated_password).deliver_later
     end
     { saved: saved, user: admin }
   end
@@ -61,7 +61,7 @@ class UserService
       manager.send_confirmation_instructions
       manager.add_role(:manager)
       manager.remove_role(:member)
-      UsersMailer.delay.notify_user_account_created(manager, generated_password)
+      UsersMailer.notify_user_account_created(manager, generated_password).deliver_later
     end
     { saved: saved, user: manager }
   end