Remove "gerrit-plugin-publish" from zuul file

It doesn't work (broken) and it's not really needed.

Change-Id: I8752643df52f5c2668f1a1deb4d7d82dbcc9968c

.zuul.yaml

diff --git a/.zuul.yaml b/.zuul.yaml
index 7004a0c..e75e16f 100644
--- a/.zuul.yaml
+++ b/.zuul.yaml
@@ -16,6 +16,3 @@
     post:
       jobs:
         - plugins-image-diff-build
-        - gerrit-plugin-publish:
-            dependencies:
-              - plugins-image-diff-build