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/post_sets/post_test.rb

@@ -6,7 +6,6 @@ module PostSets
       setup do
         @user = FactoryBot.create(:user)
         CurrentUser.user = @user
-        CurrentUser.ip_addr = "127.0.0.1"
 
         @post_1 = FactoryBot.create(:post, :tag_string => "a")
         @post_2 = FactoryBot.create(:post, :tag_string => "b")
@@ -15,7 +14,6 @@ module PostSets
 
       teardown do
         CurrentUser.user = nil
-        CurrentUser.ip_addr = nil
       end
 
       context "a set for page 2" do