LU-16335 mdt: skip target check for rm_entry

LU-16335 mdt: skip target check for rm_entry

For "lfs rm_entry", target may not exist, sanity check of it may fail
thus causes rm_entry fail.

Add sanity 832.

Signed-off-by: Lai Siyao <lai.siyao@whamcloud.com>
Change-Id: I824c7581af05c7494cf03c0c9bc999ca1abfec01
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/49329
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Qian Yingjin <qian@ddn.com>
Reviewed-by: jsimmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>