Remove CurrentUser.ip_addr.

Remove the `CurrentUser.ip_addr` global variable and replace it with
`request.remote_ip`. Before we had to track the current user's IP in a
global variable so that when we edited a post for example, we could pass
down the user's IP to the model and save it in the post_versions table.
Now that we now longer save IPs in version tables, we don't need a global
variable to get access to the current user's IP outside of controllers.

app/models/application_record.rb

@@ -217,14 +217,13 @@ class ApplicationRecord < ActiveRecord::Base
         end
 
         current_user = CurrentUser.user
-        current_ip = CurrentUser.ip_addr
 
         find_in_batches(batch_size: batch_size, error_on_ignore: true) do |batch|
           Parallel.each(batch, in_processes: in_processes, in_threads: in_threads) do |record|
             # XXX In threaded mode, the current user isn't inherited from the
             # parent thread because the current user is a thread-local
             # variable. Hence, we have to set it explicitly in the child thread.
-            CurrentUser.scoped(current_user, current_ip) do
+            CurrentUser.scoped(current_user) do
               yield record
             end
           end