autopkgtest: systemd no longer supports sysv scripts

Remove test case from the spec-service-systemd suite.

246s   19) Command "puppet apply --debug --detailed-exitcodes -e
"service { 'dep8-sysv-only' : ensure => stopped, enable => false,
provider => 'systemd' }"" exit_status is expected to eq 2
246s       Failure/Error: its(:exit_status) { should eq 2 }
246s
246s         expected: 2
246s              got: 0
246s
246s         (compared using ==)
246s
246s       # ./spec/service-systemd/systemd_spec.rb:42:in `block (4
levels) in <top (required)>'
246s
246s   20) Command "systemctl is-enabled dep8-sysv-only" stdout is
expected to match /^disabled/
246s       Failure/Error: its(:stdout) { should match /^disabled/ }
246s         expected "not-found\n" to match /^disabled/
246s         Diff:
246s         @@ -1 +1 @@
246s         -/^disabled/
246s         +not-found
246s         /bin/sh -c systemctl\ is-enabled\ dep8-sysv-only
246s         not-found

Closes: #1129078