task/install: rm {proj}.list is idempotent
task/install: rm {proj}.list is idempotent

It does not matter if the {proj}.list file can't be removed because it
does not exist.

Signed-off-by: Loic Dachary <b6eae37fc74638590e3f9030895d42446505d41b@dachary.org>

ivotron/teuthology,robbat2/teuthology,michaelsevilla/teuthology,SUSE/teuthology,caibo2014/teuthology,SUSE/teuthology,SUSE/teuthology,dmick/teuthology,dmick/teuthology,ktdreyer/teuthology,dreamhost/teuthology,ceph/teuthology,robbat2/teuthology,ceph/teuthology,ivotron/teuthology,caibo2014/teuthology,ktdreyer/teuthology,dmick/teuthology,michaelsevilla/teuthology,dreamhost/teuthology