drm/i915: Drop unecessary complexity from psr_inactivate
It's not needed and further more will get in the way of a sane
locking scheme - psr_exit _can't_ take modeset locks due to lock
inversion, and at least once dp mst hits the connector list
is no longer static.
But since we track all state in dev_priv->psr there is no need
at all.