Fix a race condition that allowed soft-deleted groups to remain in the database.

The intended flow is:

  Soft-delete group (sync) -> Delete group projects (async) -> Hard-delete group (async)

The soft-delete was run in a transaction, which was committed only after
the async job (for hard-deletion) was kicked off. There was a race
condition here - the soft-delete transaction could complete _after_ the
hard delete completed, leaving a soft-deleted record in the database.

This commit removes this race condition. There is no need to run the
soft-delete in a transaction. The soft-delete completes before the async
job is kicked off.

app/services/destroy_group_service.rb

@@ -6,13 +6,11 @@ class DestroyGroupService
   end
 
   def async_execute
-    group.transaction do
     # Soft delete via paranoia gem
     group.destroy
     job_id = GroupDestroyWorker.perform_async(group.id, current_user.id)
     Rails.logger.info("User #{current_user.id} scheduled a deletion of group ID #{group.id} with job ID #{job_id}")
   end
-  end
 
   def execute
     group.projects.each do |project|