LU-13326 mds: remove MDS_SETATTR_PORTAL and service

LU-13326 mds: remove MDS_SETATTR_PORTAL and service

Remove the MDS_SETATTR_PORTAL and the service threads listening on
this portal since they are unused since Lustre 2.1 and are no longer
needed.

Remove module tunables related to the mds_attr service threads:
- mds_attr_num_threads
- mds_attr_cpu_bind
- mds_attr_num_cpts

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I64f4f3f0004e1895ef7b49b31a4ad687a1abcca2
Reviewed-on: https://review.whamcloud.com/37798
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Lai Siyao <lai.siyao@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>