Adopt to latest puppetlabs/apt changes

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

see also puppetlabs#738 (comment)

Author: bastelfreak

spec/classes/puppet_agent_osfamily_debian_spec.rb

@@ -58,15 +58,13 @@
         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',
                 })
       }