Remove an unneeded config from .rubocop.yml

rubocop-rails repo does not have spec/rubocop/cop/style/ip_addresses_spec.rb.

Author: koic

.rubocop.yml

@@ -30,11 +30,6 @@ Style/FormatStringToken:
   Exclude:
     - spec/**/*
 
-Style/IpAddresses:
-  # The test for this cop includes strings that would cause offenses
-  Exclude:
-  - spec/rubocop/cop/style/ip_addresses_spec.rb
-
 Layout/AlignHash:
   EnforcedHashRocketStyle:
     - key