alphabetize and uniquify cop config in .rubocopy.yml

[faisal]

Rubocop now gives us a warning:

$ be rubocop            
.rubocop.yml:19: `Metrics/MethodLength` is concealed by line 96
Inspecting 116 files
....................................................................................................................

116 files inspected, no offenses detected

This PR does two things:

1. It unifies the Metrics/MethodLength configuration (which was redundant, as it happens).
2. It sorts all the cop configurations to be alphabetical.

Check list:

• Add an entry to the changelog
• Squash all commits into a single one
• Describe your PR, link issues, etc.

[faisal]

Would we be happier if this were one commit to deal with Metrics/MethodLength and then a second to sort the cops?