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/factories/post.rb

@@ -3,7 +3,7 @@ FactoryBot.define do
     sequence :md5 do |n|
       n.to_s
     end
-    uploader :factory => :user
+    uploader
     uploader_ip_addr {"127.0.0.1"}
     tag_string {"tag1 tag2"}
     tag_count {2}

test/factories/user.rb

@@ -1,5 +1,5 @@
 FactoryBot.define do
-  factory(:user, aliases: [:creator, :updater]) do
+  factory(:user, aliases: [:creator, :updater, :uploader]) do
     sequence :name do |n|
       "user#{n}"
     end

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