ci-dockerfiles-*: Remove silent-start

Both of these jobs are long-running, so it's really confusing that a CI
build start notice isn't posted as a gerrit comment, as for other jobs.

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Change-Id: I8228728d23c60fdd373596a9bf80371618f8c9d5
2 files changed