tests/pm_pc8: remove sleep() call when setting up the environment

tests/pm_pc8: remove sleep() call when setting up the environment

This sleep was added because sometimes we didn't reach PC8+
residencies, but it was still not enough to prevent the problem every
time, and it is really not needed most of the times. I have
investigated more and it seems that we only have to wait until after
some minutes have past since the machine booted. So just remove the
sleep for now since when you run each subtest in a separate process,
you end up having to sleep at every subtest.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>