Remove nova cert from devstack

As a followup to I2c78a0c6599b92040146cf9f0042cff8fd2509c3, the nova
cert service should be removed from devstack.

Without this fix, stacking will fail is USE_SCREEN=True

Change-Id: I115580352fa380b896bae290f9a4efbfe4ff0dfd
diff --git a/doc/source/guides/devstack-with-lbaas-v2.rst b/doc/source/guides/devstack-with-lbaas-v2.rst
index 21bea99..4ed64bf 100644
--- a/doc/source/guides/devstack-with-lbaas-v2.rst
+++ b/doc/source/guides/devstack-with-lbaas-v2.rst
@@ -45,7 +45,7 @@
     # Horizon
     ENABLED_SERVICES+=,horizon
     # Nova
-    ENABLED_SERVICES+=,n-api,n-crt,n-cpu,n-cond,n-sch
+    ENABLED_SERVICES+=,n-api,n-cpu,n-cond,n-sch
     # Glance
     ENABLED_SERVICES+=,g-api,g-reg
     # Neutron