Remove the react-rails gem (#2801)

* Remove react-rails gem

* Fix broken view spec

spec/views/about/show.html.haml_spec.rb

@@ -1,9 +1,11 @@
-require 'rails_helper'
-$LOAD_PATH << '../lib'
-require 'tag_manager'
+# frozen_string_literal: true
 
-describe 'about/show.html.haml' do
+require 'rails_helper'
+
+describe 'about/show.html.haml', without_verify_partial_doubles: true do
   before do
+    allow(view).to receive(:site_hostname).and_return('example.com')
+    allow(view).to receive(:site_title).and_return('example site')
   end
 
   it 'has valid open graph tags' do