Remove nova_cert option

The nova-cert service was removed from nova during Pike cycle[1] and is
no longer available since 16.0.0 release. Because Pike and older
releases are no longer supported, the option can be removed now.

[1] https://review.opendev.org/c/openstack/nova/+/459460

Change-Id: If520dc802bced4acfddd75a05a31dd83bc8c6354
diff --git a/releasenotes/notes/remove-nova_cert-e2ee70a40e117e8a.yaml b/releasenotes/notes/remove-nova_cert-e2ee70a40e117e8a.yaml
new file mode 100644
index 0000000..1a292f0
--- /dev/null
+++ b/releasenotes/notes/remove-nova_cert-e2ee70a40e117e8a.yaml
@@ -0,0 +1,6 @@
+---
+upgrade:
+  - |
+    The deprecated ``[compute-feature-enabled] nova_cert`` option has been
+    removed. The nova-cert service was removed from nova in 16.0.0 release.
+    Tests of compute root certificates API have also been removed.