backports unit tests: delete linuxmint tests

Linux Mint is not listed as supported in the metadata.json file, so we
shouldn't carry tests for it (which are using facts for an end-of-life
release).

spec/classes/apt_backports_spec.rb

@@ -146,88 +146,6 @@
     end
   end
 
-  describe 'linuxmint tests' do
-    let(:facts) do
-      {
-        os: {
-          family: 'Debian',
-          name: 'LinuxMint',
-          release: {
-            major: '17',
-            full: '17'
-          },
-          distro: {
-            codename: 'qiana',
-            id: 'LinuxMint'
-          }
-        }
-      }
-    end
-
-    context 'with all the needed things set' do
-      let(:params) do
-        {
-          location: 'http://archive.ubuntu.com/ubuntu',
-          release: 'trusty-backports',
-          repos: 'main universe multiverse restricted',
-          key: '630239CC130E1A7FD81A27B140976EAF437D05B5'
-        }
-      end
-
-      it {
-        expect(subject).to contain_apt__source('backports').with(
-          location: 'http://archive.ubuntu.com/ubuntu',
-          key: '630239CC130E1A7FD81A27B140976EAF437D05B5',
-          repos: 'main universe multiverse restricted',
-          release: 'trusty-backports',
-          pin: { 'priority' => 200, 'release' => 'trusty-backports' },
-        )
-      }
-    end
-
-    context 'with missing location' do
-      let(:params) do
-        {
-          release: 'trusty-backports',
-          repos: 'main universe multiverse restricted',
-          key: '630239CC130E1A7FD81A27B140976EAF437D05B5'
-        }
-      end
-
-      it do
-        expect(subject).to raise_error(Puppet::Error, %r{If not on Debian or Ubuntu, you must explicitly pass location, release, and repos})
-      end
-    end
-
-    context 'with missing release' do
-      let(:params) do
-        {
-          location: 'http://archive.ubuntu.com/ubuntu',
-          repos: 'main universe multiverse restricted',
-          key: '630239CC130E1A7FD81A27B140976EAF437D05B5'
-        }
-      end
-
-      it do
-        expect(subject).to raise_error(Puppet::Error, %r{If not on Debian or Ubuntu, you must explicitly pass location, release, and repos})
-      end
-    end
-
-    context 'with missing repos' do
-      let(:params) do
-        {
-          location: 'http://archive.ubuntu.com/ubuntu',
-          release: 'trusty-backports',
-          key: '630239CC130E1A7FD81A27B140976EAF437D05B5'
-        }
-      end
-
-      it do
-        expect(subject).to raise_error(Puppet::Error, %r{If not on Debian or Ubuntu, you must explicitly pass location, release, and repos})
-      end
-    end
-  end
-
   describe 'validation' do
     let(:facts) do
       {