Remove views for plugin jobs of old branches

The branches <= stable-2.12 are not being built anymore on the CI, but
the corresponding views were still created.

This change removes these views.

Change-Id: I087bfc045b044d433834bc72364841a64b0ff477
diff --git a/jenkins/gerrit-buck-bazel-plugin-template.yaml b/jenkins/gerrit-buck-bazel-plugin-template.yaml
index a28f4d8..a148600 100644
--- a/jenkins/gerrit-buck-bazel-plugin-template.yaml
+++ b/jenkins/gerrit-buck-bazel-plugin-template.yaml
@@ -88,6 +88,3 @@
       - stable-2.15
       - stable-2.14
       - stable-2.13
-      - stable-2.12
-      - stable-2.11
-      - stable-2.10