Revert #10957 (rubocop-rails) which is incompatible with CodeClimate (#10965)

.rubocop.yml

@@ -1,6 +1,3 @@
-require:
-  - rubocop-rails
-
 AllCops:
   TargetRubyVersion: 2.3
   Exclude:

Gemfile

@@ -129,7 +129,6 @@ group :development do
   gem 'letter_opener_web', '~> 1.3'
   gem 'memory_profiler'
   gem 'rubocop', '~> 0.71', require: false
-  gem 'rubocop-rails', '~> 2.0', require: false
   gem 'brakeman', '~> 4.5', require: false
   gem 'bundler-audit', '~> 0.6', require: false
 

Gemfile.lock

@@ -531,9 +531,6 @@ GEM
       rainbow (>= 2.2.2, < 4.0)
       ruby-progressbar (~> 1.7)
       unicode-display_width (>= 1.4.0, < 1.7)
-    rubocop-rails (2.0.0)
-      rack (>= 2.0)
-      rubocop (>= 0.70.0)
     ruby-progressbar (1.10.1)
     ruby-saml (1.9.0)
       nokogiri (>= 1.5.10)
@@ -738,7 +735,6 @@ DEPENDENCIES
   rspec-rails (~> 3.8)
   rspec-sidekiq (~> 3.0)
   rubocop (~> 0.71)
-  rubocop-rails (~> 2.0)
   sanitize (~> 5.0)
   sidekiq (~> 5.2)
   sidekiq-bulk (~> 0.2.0)