Remove high-availability Zuul project

The high-availability plugin is already verified by Gerrit-CI.

Change-Id: I65a8b178f70983631b0c2912d8170a4a010073ab
diff --git a/zuul/main.yaml b/zuul/main.yaml
index 403c88f..1aafdf2 100644
--- a/zuul/main.yaml
+++ b/zuul/main.yaml
@@ -43,7 +43,6 @@
           - plugins/go-import
           - plugins/healthcheck
           - plugins/heartbeat
-          - plugins/high-availability
           - plugins/imagare
           - plugins/its-base
           - plugins/javamelody