Adopt to latest puppetlabs/apt changes

for the changes in puppetlabs/puppetlabs-apt@1e1baad#diff-792ade83ea45b5c6696875678e6e7cc52f4a105db6ed4d8b6f2933ec5d7d6f3bR25-R26

see also #738 (comment)

Author: bastelfreak

manifests/osfamily/debian.pp

@@ -60,13 +60,11 @@
         # Pass in an empty content string since apt requires it even though we are removing it
         apt::setting { 'list-puppet-enterprise-installer':
           ensure  => absent,
-          content => '',
         }
 
         apt::setting { 'conf-pe-repo':
           ensure   => absent,
           priority => '90',
-          content  => '',
         }
       } else {
         $source = $puppet_agent::apt_source

spec/classes/puppet_agent_osfamily_debian_spec.rb

@@ -58,16 +58,14 @@
         is_expected.to contain_apt__setting('conf-pe-repo')
           .with({
                   'priority' => 90,
-                  'content'  => '',
                   'ensure'   => 'absent',
                 })
       }
 
       it {
         is_expected.to contain_apt__setting('list-puppet-enterprise-installer')
           .with({
-                  'content' => '',
-                  'ensure'  => 'absent',
+                  'ensure' => 'absent',
                 })
       }
     end