drm/xe: Remove unused extension definition

The vm_create ioctl function doesn't accept any extension.
Remove this left over.
A backward compatible change.

Cc: Francois Dugast <francois.dugast@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Francois Dugast <francois.dugast@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>

include/uapi/drm/xe_drm.h

@@ -643,7 +643,6 @@ struct drm_xe_ext_set_property {
 };
 
 struct drm_xe_vm_create {
-#define DRM_XE_VM_EXTENSION_SET_PROPERTY	0
 	/** @extensions: Pointer to the first extension struct, if any */
 	__u64 extensions;