drm/vgem: Drop drm_gem_prime_export

They're the default.

Aside: Would be really nice to switch the others over to
drm_gem_object_funcs.
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190614203615.12639-37-daniel.vetter@ffwll.ch

drivers/gpu/drm/vgem/vgem_drv.c

@@ -445,7 +445,6 @@ static struct drm_driver vgem_driver = {
 	.gem_prime_pin = vgem_prime_pin,
 	.gem_prime_unpin = vgem_prime_unpin,
 	.gem_prime_import = vgem_prime_import,
-	.gem_prime_export = drm_gem_prime_export,
 	.gem_prime_import_sg_table = vgem_prime_import_sg_table,
 	.gem_prime_get_sg_table = vgem_prime_get_sg_table,
 	.gem_prime_vmap = vgem_prime_vmap,