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.

Lustre-change: https://review.whamcloud.com/49329
Lustre-commit: ae98c5fdaaf37daeb328b7110cbcf42754752c9d

Signed-off-by: Lai Siyao <lai.siyao@whamcloud.com>
Change-Id: I824c7581af05c7494cf03c0c9bc999ca1abfec01
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Qian Yingjin <qian@ddn.com>
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/49712
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>