Remove jobs to build saml-plugin for stable-2.11/2.12

Change-Id: I7494c75d3fa8d293c39494c8927e57103230acbc
diff --git a/jenkins/gerrit-plugin-saml.yaml b/jenkins/gerrit-plugin-saml.yaml
index 673282a..d2f80a2 100644
--- a/jenkins/gerrit-plugin-saml.yaml
+++ b/jenkins/gerrit-plugin-saml.yaml
@@ -6,7 +6,3 @@
             - master
             - stable-2.15
             - stable-2.14
-      - 'plugin-{name}-sbt-{branch}':
-          branch:
-            - stable-2.12
-            - stable-2.11