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.

db/populate.rb

@@ -24,7 +24,6 @@ FAVORITES    = ENV.fetch("FAVORITES",    POSTS * 5.0).to_i
 DEFAULT_PASSWORD = ENV.fetch("DEFAULT_PASSWORD", "password")
 
 CurrentUser.user = User.system
-CurrentUser.ip_addr = "127.0.0.1"
 
 def populate_users(n, password: DEFAULT_PASSWORD)
   puts "*** Creating users ***"