Remove 'dvr_extra_resources' option

The dvr_extra_resources option had been added since the commit
Ib1a6007bbd65182743e1f1ed5819134d748e8d92 . This option was for extra
resources which were provisioned to bind a router to Neutron L3 agent.
The extra resources need to be provisioned in Liberty release or older,
and are not required since Mitaka release. Current Tempest doesn't
support Liberty, so this patch removes the config option from Tempest.

Change-Id: I1eb228559a170a2a157a180ac8404bcbd5efd062
diff --git a/releasenotes/notes/remove-deprecated-dvr_extra_resources-option-e8c441c38eab7ddd.yaml b/releasenotes/notes/remove-deprecated-dvr_extra_resources-option-e8c441c38eab7ddd.yaml
new file mode 100644
index 0000000..889e862
--- /dev/null
+++ b/releasenotes/notes/remove-deprecated-dvr_extra_resources-option-e8c441c38eab7ddd.yaml
@@ -0,0 +1,8 @@
+---
+upgrade:
+  - |
+    The deprecated config option 'dvr_extra_resources' from network group has been removed.
+    This option was for extra resources which were provisioned to bind a router to Neutron
+    L3 agent. The extra resources need to be provisioned in Liberty release or older,
+    and are not required since Mitaka release. Current Tempest doesn't support Liberty, so
+    this option has been removed from Tempest.