drm/i915: remove i915_vma::obj_hash

i915_vma::obj_hash was never used since its addition in commit
4ff4b44c (drm/i915: Store a direct lookup from object handle to
vma). Drop it.

Found by https://github.com/jirislaby/clang-struct.
Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: intel-gfx@lists.freedesktop.org
Acked-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240216065326.6910-21-jirislaby@kernel.org

drivers/gpu/drm/i915/i915_vma_types.h

@@ -290,7 +290,6 @@ struct i915_vma {
 
 	struct list_head obj_link; /* Link in the object's VMA list */
 	struct rb_node obj_node;
-	struct hlist_node obj_hash;
 
 	/** This vma's place in the eviction list */
 	struct list_head evict_link;