Remove jobs for neutron-fwaas master branch

Neutron-fwaas is going to be deprecated in master branch with [1].

[1] https://review.opendev.org/#/c/735828/

Depends-On: https://review.opendev.org/#/c/735829/

Change-Id: I432523933a7f930932fd2fd7d25b948b02f275f5
diff --git a/zuul.d/train_jobs.yaml b/zuul.d/train_jobs.yaml
index f2dd6b7..132873b 100644
--- a/zuul.d/train_jobs.yaml
+++ b/zuul.d/train_jobs.yaml
@@ -144,7 +144,7 @@
 
 - job:
     name: neutron-tempest-plugin-fwaas-train
-    parent: neutron-tempest-plugin-fwaas
+    parent: neutron-tempest-plugin-fwaas-ussuri
     override-checkout: stable/train
     vars:
       branch_override: stable/train