PM / core: Drop unused internal functions for pm_qos sysfs

The functions pm_qos_sysfs_add|remove() are available as inline functions
only while CONFIG_PM is unset, but are not being used. Likely they are a
leftover from an earlier cleanup in the past, anyway let's drop them.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>