tests: fix null uploader_ip_addr exceptions in create(:post).

Caused by a change in FactoryBot 5. Associations in factories are now
constructed using the same strategy as the base object, meaning that
using `build` to construct an object will also construct the
associations using `build`. This meant that overriding `create` to do
`build` + `save` broke the way that associations were constructed.

https://github.com/thoughtbot/factory_bot/blob/master/GETTING_STARTED.md#associations

test/test_helper.rb

@@ -26,13 +26,6 @@ Shoulda::Matchers.configure do |config|
 end
 
 module TestHelpers
-  def create(factory_bot_model, params = {})
-    record = FactoryBot.build(factory_bot_model, params)
-    record.save
-    raise ActiveRecord::RecordInvalid.new(record) if record.errors.any?
-    record
-  end
-
   def as(user, &block)
     CurrentUser.as(user, &block)
   end