Remove outdated regression test

Per https://github.com/rails-api/active_model_serializers/pull/1390#discussion_r48322329

test/active_model_serializers/test/serializer_test.rb

@@ -6,7 +6,6 @@ module ActiveModelSerializers
       include ActiveModelSerializers::Test::Serializer
 
       class MyController < ActionController::Base
-        TEMPLATE_NAME = 'template'
         def render_using_serializer
           render json: Profile.new(name: 'Name 1', description: 'Description 1', comments: 'Comments 1')
         end
@@ -15,11 +14,6 @@ module ActiveModelSerializers
         def render_some_text
           Rails.version > '4.1' ? render(plain: 'ok') : render(text: 'ok')
         end
-
-        def render_a_template
-          prepend_view_path './test/fixtures'
-          render template: TEMPLATE_NAME
-        end
       end
 
       tests MyController
@@ -64,23 +58,6 @@ module ActiveModelSerializers
         end
         assert_match 'assert_serializer only accepts a String, Symbol, Regexp, ActiveModel::Serializer, or nil', e.message
       end
-
-      def test_does_not_overwrite_notification_subscriptions
-        payloads = []
-        event_name = '!render_template.action_view'
-        ActiveSupport::Notifications.subscribe(event_name) do |_name, _start, _finish, _id, payload|
-          payloads << payload
-        end
-
-        get :render_a_template
-
-        assert_equal 1, payloads.size, 'Only expected one template rendering to be registered'
-        payload = payloads.first
-        assert_equal MyController::TEMPLATE_NAME, payload[:virtual_path]
-        assert_match %r{test/fixtures/#{MyController::TEMPLATE_NAME}.html.erb}, payload[:identifier]
-      ensure
-        ActiveSupport::Notifications.unsubscribe(event_name)
-      end
     end
   end
 end

test/fixtures/template.html.erb

@@ -1 +0,0 @@
-<p>Hello.</p>