drm/xe/uapi: Remove DRM_XE_VM_BIND_FLAG_ASYNC comment left over

This is a comment left over of commit d3d76739
("drm/xe/uapi: Remove sync binds").

Fixes: d3d76739 ("drm/xe/uapi: Remove sync binds")
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>

include/uapi/drm/xe_drm.h

@@ -832,7 +832,6 @@ struct drm_xe_vm_destroy {
  *
  * and the @flags can be:
  *  - %DRM_XE_VM_BIND_FLAG_READONLY
- *  - %DRM_XE_VM_BIND_FLAG_ASYNC
  *  - %DRM_XE_VM_BIND_FLAG_IMMEDIATE - Valid on a faulting VM only, do the
  *    MAP operation immediately rather than deferring the MAP to the page
  *    fault handler.