Enable Rubocop/Rails cops (#2125) [ci skip]

.rubocop.yml

@@ -97,10 +97,6 @@ Metrics/CyclomaticComplexity:
     of test cases needed to validate a method.
   Enabled: false
 
-Rails/Delegate:
-  Description: 'Prefer delegate method for delegations.'
-  Enabled: false
-
 Style/Documentation:
   Description: 'Document classes and non-namespace modules.'
   Enabled: false
@@ -411,48 +407,18 @@ Performance/StringReplacement:
 
 # Rails
 
-Rails/ActionFilter:
-  Description: 'Enforces consistent use of action filter methods.'
-  Enabled: false
-
 Rails/Date:
   Description: >-
     Checks the correct usage of date aware methods,
     such as Date.today, Date.current etc.
   Enabled: true
 
-Rails/FindBy:
-  Description: 'Prefer find_by over where.first.'
-  Enabled: false
-
-Rails/FindEach:
-  Description: 'Prefer all.find_each over all.find.'
-  Enabled: false
-
 Rails/HasAndBelongsToMany:
   Description: 'Prefer has_many :through to has_and_belongs_to_many.'
   Enabled: false
 
-Rails/Output:
-  Description: 'Checks for calls to puts, print, etc.'
-  Enabled: false
-
-Rails/ReadWriteAttribute:
-  Description: >-
-    Checks for read_attribute(:attr) and
-    write_attribute(:attr, val).
-  Enabled: false
-
-Rails/ScopeArgs:
-  Description: 'Checks the arguments of ActiveRecord scopes.'
-  Enabled: false
-
 Rails/TimeZone:
   Description: 'Checks the correct usage of time zone aware methods.'
   StyleGuide: 'https://github.com/bbatsov/rails-style-guide#time'
   Reference: 'http://danilenko.org/2012/7/6/rails_timezones'
   Enabled: false
-
-Rails/Validation:
-  Description: 'Use validates :attribute, hash of validations.'
-  Enabled: false