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/saved_search_test.rb

@@ -5,7 +5,6 @@ class SavedSearchTest < ActiveSupport::TestCase
     super
     @user = FactoryBot.create(:user)
     CurrentUser.user = @user
-    CurrentUser.ip_addr = "127.0.0.1"
     @mock_redis = MockRedis.new
     SavedSearch.stubs(:redis).returns(@mock_redis)
   end
@@ -13,7 +12,6 @@ class SavedSearchTest < ActiveSupport::TestCase
   def teardown
     super
     CurrentUser.user = nil
-    CurrentUser.ip_addr = nil
   end
 
   context ".labels_for" do