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/controllers/comments_controller.rb

@@ -43,7 +43,7 @@ class CommentsController < ApplicationController
   end
 
   def create
-    @comment = authorize Comment.new(creator: CurrentUser.user, creator_ip_addr: CurrentUser.ip_addr)
+    @comment = authorize Comment.new(creator: CurrentUser.user, creator_ip_addr: request.remote_ip)
     @comment.update(permitted_attributes(@comment))
     flash[:notice] = @comment.valid? ? "Comment posted" : @comment.errors.full_messages.join("; ")
     respond_with(@comment) do |format|