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.

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>