ipmi:ssif: Remove rtc_us_timer

[ Upstream commit 9e8b8992 ]

It was cruft left over from older handling of run to completion.

Cc: stable@vger.kernel.org
Signed-off-by: Corey Minyard <cminyard@mvista.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>