drm/i915: Remove manual save/resume of fence register state

Since we always reload the fence register state on runtime resume,
having it explicitly in the S0ix resume code is redundant. Indeed, it
is not even being used!

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200316113846.4974-3-chris@chris-wilson.co.uk