greybus: remove submit_svc from the host driver

The callback is never used anymore, so remove it from struct
greybus_host_driver as well as from the es1 and es2 drivers.

Tested-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>