Remove openssh-server's init script

We are moving openssh out of platform/init. openssh-server.conf now lives in
openssh-server-init's package.

BUG=chromium:350607
TEST=build chromeos-init and openssh-server-init. openssh-server.conf is still
installed and owned by openssh-server-init.

CQ-DEPEND=Ie8e7d30ef13d74ff35c52f81b9d7008e39c70764

Change-Id: I8d279bfdec8cac026653e15eb38bec369447abbf
Reviewed-on: https://chromium-review.googlesource.com/189491
Reviewed-by: Simran Basi <sbasi@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Tested-by: Bertrand Simonnet <bsimonnet@chromium.org>
Commit-Queue: Bertrand Simonnet <bsimonnet@chromium.org>