Revert "image-diff: set bazelisk_test_targets to """

This reverts commit 7dd714d7ab7633eda0a8c2954f553f80b720e2c2.

Reason for revert: Doesn't work. I think this will only work with "job".

Change-Id: Ie8f0bf3bcccee85eaef104d3c197eaf5b72a18cf

zuul.d/projects.yaml

diff --git a/zuul.d/projects.yaml b/zuul.d/projects.yaml
index 90477ef..9c7584c 100644
--- a/zuul.d/projects.yaml
+++ b/zuul.d/projects.yaml
@@ -177,7 +177,6 @@
     vars:
       bazelisk_artifacts:
         - "bazel-bin/plugins/{{ gerrit_plugin }}/{{ gerrit_plugin }}.js"
-      bazelisk_test_targets: ""
     templates:
       - non-core-plugin