remove useless test gem

Gemfile

@@ -126,7 +126,6 @@ end
 
 group :test do
   gem 'shoulda'
-  gem 'shoulda-callback-matchers', '~> 1.1.1'
 end
 
 gem 'streamio-ffmpeg', '~> 1.0.0'

Gemfile.lock

@@ -403,8 +403,6 @@ GEM
     shoulda (3.5.0)
       shoulda-context (~> 1.0, >= 1.0.1)
       shoulda-matchers (>= 1.4.1, < 3.0)
-    shoulda-callback-matchers (1.1.3)
-      activesupport (>= 3)
     shoulda-context (1.2.1)
     shoulda-matchers (2.8.0)
       activesupport (>= 3.0.0)
@@ -528,7 +526,6 @@ DEPENDENCIES
   searchkick
   select2-rails
   shoulda
-  shoulda-callback-matchers (~> 1.1.1)
   sidekiq
   sinatra
   slim

test/test_helper.rb

 ENV['RAILS_ENV'] ||= 'test'
 require File.expand_path('../../config/environment', __FILE__)
 require 'rails/test_help'
-require 'shoulda-callback-matchers'
 require 'minitest/mock'
 
 class ActiveSupport::TestCase