drm/i915/overlay: Remove GPU hang snapshot stuff

drm/i915/overlay: Remove GPU hang snapshot stuff

The overlay snapshot stuff is a bit annoying because some of
it more or less of belongs on the gt side, and some on the
display side. Remove the whole thing to avoid having to deal
with it when splitting the overlay code around the i915
vs. display boundary. I don't think I've ever actually used
this for anything, so no real loss from my POV. And it can
always be resurrected later should the need arise.

v2: Rebase due to kmalloc_obj()

Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patch.msgid.link/20260226100738.29997-2-ville.syrjala@linux.intel.com