diag: Remove unnecessary workqueue flush while peripheral ssr

When Peripheral is going down as part of ssr, flushing the
scheduled workqueues is not needed as part of cleanup.

Change-Id: Id5222d6f65166cd8c8ad770bfdb56253a5284c8e
Signed-off-by: Manoj Prabhu B <bmanoj@codeaurora.org>