Use JJB --delete-old option to keep job list clean

Use JJB's update --delete-old option to keep the list of jobs in Jenkins
as small as possible. This will delete any jobs not known in the JJB
config files.

Change-Id: I348e33f69f74f8ae8d4a87db85e1336d2cf44368
Merge "Use JJB --delete-old option to keep job list clean"