Remove base job

With I26ffddad8358c156cfac749ce98af70f3447f671, base jobs may no
longer be defined in untrusted projects, and we want zuul-jobs
to be usable as an untrusted project.  Remove the base job from
here; later we can add it to zuul-base-jobs and treat that as a
config repo.

Change-Id: I9688fd844776c8fc5cf9bdd555ec3bcde7ead054
Depends-On: I26ffddad8358c156cfac749ce98af70f3447f671

zuul.yaml

@@ -1,30 +1,5 @@
-# TODO: further parameterize the base job and roles so that it can
-# include log publishing and nodeset defaults once Zuul supports
-# site-local variables.
-- job:
-    name: base
-    description: |
-      A sample base job.
-
-      Zuul installations should override this job using the project
-      "shadow" functionality.
-
-      All jobs ultimately inherit from this.  It runs a pre-playbook
-      which copies all of the job's prepared git repos on to all of
-      the nodes in the nodeset and sets the default timeout value.
-
-      Zuul installations should add a log publishing post playbook to
-      this job, and may wish to supply a default nodeset and adjust
-      the timeout values.
-    pre-run: playbooks/base/pre
-    post-run: playbooks/base/post-ssh
-    roles:
-      - zuul: openstack-infra/zuul-jobs
-    timeout: 1800
-
 - job:
     name: unittests
-    parent: base
     description: |
       Perform setup common to all unit test jobs.