Remove Rails/* cop configurations

Funny story: we had a bunch of Rails/* cops in the config all along and
I was always impressed how they didn't explode for non-Rails projects,
but it turns out that they were just never actually running for some 
reason or another.

Rather than try to slam them in now just to try to get upgraded to the
latest rubocop, the most prudent thing is to remove them from the config
to spare our users the postinstall warning they'll get about all these
Rails/* cops we were apparently never invoking anyway.

Maybe it'll make sense to incorporate them at some point (like 
dynamically require the cop config if `defined?(Railtie)`, but there's
no reason it needs to be today as part of this PR to upgrade rub{y,ocop}

config/base.yml

@@ -1,6 +1,5 @@
 require:
   - rubocop-performance
-  - rubocop-rails
 
 AllCops:
   # Prevent RuboCop from exploding when it finds an older-than-2.3 .ruby-version
@@ -692,199 +691,6 @@ Performance/UnfreezeString:
 Performance/UriDefaultParser:
   Enabled: true
 
-Rails/ActionFilter:
-  Enabled: true
-  EnforcedStyle: action
-  Include:
-    - app/controllers/**/*.rb
-
-Rails/ActiveRecordAliases:
-  Enabled: true
-
-Rails/ActiveSupportAliases:
-  Enabled: true
-
-Rails/ApplicationJob:
-  Enabled: true
-
-Rails/ApplicationRecord:
-  Enabled: true
-
-Rails/AssertNot:
-  Enabled: true
-  Include:
-    - '**/test/**/*'
-
-Rails/Blank:
-  Enabled: true
-  # Convert usages of `nil? || empty?` to `blank?`
-  NilOrEmpty: true
-  # Convert usages of `!present?` to `blank?`
-  NotPresent: true
-  # Convert usages of `unless present?` to `if blank?`
-  UnlessPresent: true
-
-Rails/BulkChangeTable:
-  Enabled: true
-  Database: null
-  Include:
-    - db/migrate/*.rb
-
-Rails/CreateTableWithTimestamps:
-  Enabled: true
-  Include:
-    - db/migrate/*.rb
-
-Rails/Date:
-  Enabled: true
-  EnforcedStyle: flexible
-
-Rails/Delegate:
-  Enabled: true
-  EnforceForPrefixed: true
-
-Rails/DelegateAllowBlank:
-  Enabled: true
-
-Rails/DynamicFindBy:
-  Enabled: true
-  Whitelist:
-    - find_by_sql
-
-Rails/EnumUniqueness:
-  Enabled: true
-  Include:
-    - app/models/**/*.rb
-
-Rails/EnvironmentComparison:
-  Enabled: true
-
-Rails/Exit:
-  Enabled: true
-  Include:
-    - app/**/*.rb
-    - config/**/*.rb
-    - lib/**/*.rb
-  Exclude:
-    - lib/**/*.rake
-
-Rails/FilePath:
-  Enabled: true
-  EnforcedStyle: arguments
-
-Rails/FindBy:
-  Enabled: true
-  Include:
-    - app/models/**/*.rb
-
-Rails/FindEach:
-  Enabled: true
-  Include:
-    - app/models/**/*.rb
-
-Rails/HasAndBelongsToMany:
-  Enabled: true
-  Include:
-    - app/models/**/*.rb
-
-Rails/HttpPositionalArguments:
-  Enabled: true
-  Include:
-    - 'spec/**/*'
-    - 'test/**/*'
-
-Rails/HttpStatus:
-  Enabled: true
-  EnforcedStyle: symbolic
-
-Rails/InverseOf:
-  Enabled: true
-  Include:
-    - app/models/**/*.rb
-
-Rails/LexicallyScopedActionFilter:
-  Enabled: true
-  Safe: false
-  Include:
-    - app/controllers/**/*.rb
-
-Rails/NotNullColumn:
-  Enabled: true
-  Include:
-    - db/migrate/*.rb
-
-Rails/Output:
-  Enabled: true
-  Include:
-    - app/**/*.rb
-    - config/**/*.rb
-    - db/**/*.rb
-    - lib/**/*.rb
-
-Rails/OutputSafety:
-  Enabled: true
-
-Rails/PluralizationGrammar:
-  Enabled: true
-
-Rails/Presence:
-  Enabled: true
-
-Rails/Present:
-  Enabled: true
-  NotNilAndNotEmpty: true
-  NotBlank: true
-  UnlessBlank: true
-
-Rails/ReadWriteAttribute:
-  Enabled: true
-  Include:
-    - app/models/**/*.rb
-
-Rails/RedundantReceiverInWithOptions:
-  Enabled: true
-
-Rails/RefuteMethods:
-  Enabled: true
-  Include:
-    - '**/test/**/*'
-
-Rails/RelativeDateConstant:
-  Enabled: true
-  AutoCorrect: false
-
-Rails/RequestReferer:
-  Enabled: true
-  EnforcedStyle: referer
-
-Rails/ReversibleMigration:
-  Enabled: true
-  Include:
-    - db/migrate/*.rb
-
-Rails/SafeNavigation:
-  Enabled: true
-  ConvertTry: false
-
-Rails/ScopeArgs:
-  Enabled: true
-  Include:
-    - app/models/**/*.rb
-
-Rails/TimeZone:
-  Enabled: true
-  EnforcedStyle: flexible
-
-Rails/UniqBeforePluck:
-  Enabled: true
-  EnforcedStyle: conservative
-  AutoCorrect: false
-
-Rails/Validation:
-  Enabled: true
-  Include:
-    - app/models/**/*.rb
-
 Security/Eval:
   Enabled: true