ci-dockerslaves-cleanup: remove missing builders

x86-11 and 12 were removed in the past, which means that
this job will hang forever waiting to acces them.  That
will block all other ci-docker.* jobs, which prevents
sanity checks and deployments from running.

This updates the cleanup job to remove the missing servers.

Signed-off-by: Kelley Spoon <kelley.spoon@linaro.org>
Change-Id: I5d5c0829bf0e986d91e268fc22dc54ed3e647fe4
diff --git a/ci-dockerslaves-cleanup.yaml b/ci-dockerslaves-cleanup.yaml
index 9d2fe66..c545b16 100644
--- a/ci-dockerslaves-cleanup.yaml
+++ b/ci-dockerslaves-cleanup.yaml
@@ -31,8 +31,6 @@
             values:
                 - aosp-x86_64-09
                 - aosp-x86_64-10
-                - x86_64-11
-                - x86_64-12
                 - x86_64-13
                 - x86_64-14
                 - x86_64-15