Removed timestamper plugin

  This plugin causes Jenkins to produce huge amount of logs
  from builds. After just two weeks we have 600GB of disk space
  consumed.

  Restore change I4b606078a42489400b222fd1c14a9785d19236b1

Change-Id: I2579e1ea5dcf7b9f0dda94ab1d7801978996f31f
diff --git a/Dockerfile b/Dockerfile
index f928360..9c9c6d7 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -105,7 +105,6 @@
         ssh-agent \
         test-stability \
         throttle-concurrents \
-        timestamper \
         workflow-cps \
         workflow-remote-loader \
         workflow-scm-step