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.

test/unit/sources/pixiv_test.rb

@@ -227,7 +227,6 @@ module Sources
       context "translating the tags" do
         setup do
           CurrentUser.user = FactoryBot.create(:user)
-          CurrentUser.ip_addr = "127.0.0.1"
 
           tags = {
             "comic" => "漫画",