Remove wrong warning logs generated by apt_preference

[grobie]

Description

Remove wrong warnings generated by apt_preference.

Issues Resolved

After upgrading out apt cookbook version from 2.7.0 to 6.1.0 we started to see many warnings in our chef-client logs during every run. In fact, chef wasn't doing any changes though.

[2017-06-20T11:50:48+00:00] WARN: Replacing jessie.pref with jessie.pref in /etc/apt/preferences.d/
[2017-06-20T11:50:48+00:00] WARN: Replacing jessie-backports.pref with jessie-backports.pref in /etc/apt/preferences.d/

Check List

• [ ] All tests pass. See https://github.com/chef-cookbooks/community_cookbook_documentation/blob/master/TESTING.MD
• [ ] New functionality includes testing.
• [ ] New functionality has been documented in the README if applicable
• [x] All commits have been signed for the Developer Certificate of Origin. See https://github.com/chef-cookbooks/community_cookbook_documentation/blob/master/CONTRIBUTING.MD