LU-10360 ldlm: remove client_import_find_conn()

LU-10360 ldlm: remove client_import_find_conn()

This function hasn't been used since Commit 37be05eca3f4 ("LU-10360
mgc: Use IR for client->MDS/OST connections").
So remove it.

Test-Parameters: trivial
Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: Idd68c2de1aba914e9017e9e8c10fbbe869ea5b26
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/50000
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: jsimmons <jsimmons@infradead.org>