Move LineLength cop from Metrics to Layout department

Follow rubocop/rubocop#7542.

This PR suppresses the following warning.

```console
% bundle exec rake
(snip)

Running RuboCop...
spec/project_spec.rb: Metrics/LineLength has the wrong namespace -
should be Layout
Inspecting 130 files
```

Author: koic

spec/project_spec.rb

@@ -65,7 +65,7 @@
         it 'has a valid URL' do
           issues.each do |issue|
             number = issue[:number].gsub(/\D/, '')
-            pattern = %r{^https://github\.com/rubocop-hq/rubocop-rails/(?:issues|pull)/#{number}$} # rubocop:disable Metrics/LineLength
+            pattern = %r{^https://github\.com/rubocop-hq/rubocop-rails/(?:issues|pull)/#{number}$} # rubocop:disable Layout/LineLength
             expect(issue[:url]).to match(pattern)
           end
         end